OK, but all I find in the PHB about bloodied is that it is the point that you are at half hit points and some abilities may be triggered by it. I don't see anything that indicates that it actually describes what it means in the game world, although I seem to remember something along the lines that it is when you can visibly see that the creature is suffering, etc.
Correct. The jargon is not tightly coupled to the fiction. The DM has a lot of latitude with the latter (even the players could have quite a bit - more on that latter).
The idea that being bloodied means that blood is spraying everywhere doesn't fit my concept of what combat looks like, particularly when all the damage has been bludgeoning, or psychic for example.
Never saw Scanners, I take it?

Seriously, though, bloodied did not mean blood spraying everywhere. For one thing, there are monsters with no blood. It was exception-based design, remember? So, if a monster had a triggered-on-bloodied no-action power that sprayed acid blood all over, then, yes, when it was bloodied, acid blood sprayed all over. OTOH, if it has a triggered-on-bloodied immediate reaction to breath acid, it didn't mean that. Because each power was an 'exception' in that 'design.'
(Full disclosure: I've never been entirely OK with 'exception based design.' )
This is a fundamental change in the game, and forces a change in my world.
No it isn't, the game still uses hps, hps still decline, and hps have always passed the half-way point in that process. Adding a jargon label for that was not a fundamental change. It's darn near a trivial change, especially since, IMX, a lot of DMs back in the day might acknowledge when a monster was 'about half down' or the like, if you asked. And, no, it doesn't force anything on your world, at all. In fact, a subtle but perhaps 'fundamental' change to the game that started with 3e, the increasing acceptance of customizing fluff & cosmetic details without having to change underlying mechanics (yes. 3e. katana-is-a-masterwork-bastard-sword), made it easier than ever to layer just the world you wanted over the D&D mechanics.
In my world dragons occasionally attack civilized areas. And armies of non-magical weapon wielding people could possibly kill a dragon, however unlikely.
Not all that unlikely, now, thanks to BA.
Again, one of the specific things that I consider a bad rule for our campaign. Plus a sword that is damaged and or broken is not color, it's a big deal if that's your only weapon.
Corroded needn't mean broken or even irreparably marred. Though that's an ability a very few creatures, like rust monsters, obviously have, and most others, like dragons, generally don't. It's not hard, in any edition, to add such an ability, though.
But why is it restricted to only this action
It's not, it could conceivably use it's reaction for something else.
and also that the rule now forces the fiction - now it's angry.
Bloodied Breath didn't make the dragon angry. The 'why' of it is color left up to the DM. That might be making the dragon angry, or it might not. Depends on the dragon & the story. It might, instead, be that the dragon was 'toying' with the party, and, when bloodied, finally realized it was in a real fight. (That's a rationale I like with solos, that they start battles wildly overconfident. But, again, it's only one possible rationale.)
In 4e the stat block lists triggers - that is something that presumably causes one of the listed actions automatically. Again, forcing my fiction.
Your presumption is mistake. Immediate actions, OAs, and even free actions are voluntary. (Well, generally, because exception based design. See disclaimer above.) Now, a no-action power might represent something that just happens automatically.
Once again, a fundamental change in the way the game works. This is one of the biggest ones that predicated bounded accuracy.
And, once again, no, i not a fundamental change in how the game works. If anything, it's a return to the way the game worked prior to 3e, with monsters being statted out quite differently from PCs. And, while 4e's tight math & consistent scaling did lead to bounded accuracy, it was in a more evolutionary rather than in the reactionary way you might be thinking. BA is also tight math & consistent scaling, just with smaller numbers - little more than a cosmetic change in some ways (in the ways that it's much more than a cosmetic change, the main manifestation is in how heavily being outnumbered tells in a 5e combat).
Because a bear is a bear is a bear. Sure you can have a juvenile bear, or an adult, or even an elderly bear. There will be some variation between one individual and another. But for a bear to be scaled up simply to be a reasonably balanced encounter for high-level PCs
Is a straw man. While you can always just change a monster's stats for no reason just to challenge your party, there's nothing in 4e (or any other edition) that obliges you to do so without providing a rationale.
Now, you /could/ legitimately re-stat a monster to work better at different levels, even the exact same individual, but, doing so didn't mean that it would...
capable of wandering through the village and causing the damage to said village of a small giant.
Not that you need stats for a creature to rampage through a village - or be killed by a few well-prepared villagers with boarspears. But, hypothetically, the standard-issue bear that you re-statted from a level 5 standard to a level 13 minion to work better in a paragon game, would still be the same level 5 standard in a heroic battle. If you wanted to play through it attacking a village with nothing more than nominally 1st-level defenders you might even stat it as 1st level elite. It'd be the same bear, worth the same 200 exp, in every case.
I know that is probably hard to grok, keep reading, it comes up again...
I'll start with it's intended as a producer of the fiction. I have stated repeatedly that's exactly what I don't want. I want the rules to adjudicate the fiction, not create it.
That's a trivially easy requirement to meet, it's just a matter of approach. What do you start with? Rules or fiction? If the former, you pick the rules elements you'll use and imagine a fictional rationale, if the latter, you imagine what you want in the fiction, and find the rules element that best models it.
Nothing new there.
You also state "if you want different fiction, you change the mechanics." Something that I also disagree with, the mechanics of the game should remain consistent no matter what. Yes, I advocate altering the mechanics with house rules so the mechanics meet your needs. But after that, they remain the same. Altering stats of a monster is not altering mechanics. It's altering the abilities of the creature.
In the above example of scaling a monster's level and secondary role in tandem, you really do alter the mechanics, not the monster. It can be the exact same monster, the same /individual/, even. The game can just model it differently depending on the role it's playing in the fiction. The same individual ('normally' a 10th level standard, worth 500exp) might be statted as a Solo when facing a 1st level party and a Minion when facing a 18th level one, for instance.
So altering monsters to suit your needs or tastes is not edition specific.
Correct! It's just more an art in some editions (1e) and more a science in others (3e). 4e and 5e are between those two extremes, with 4e closer to science and 5e closer to art. Well, maybe technical exercise more than science.
You state that 4e is designed to only tell you about the combat info in the stat blocks, leaving the rest to the DM. ... the assumption and design intent is that everything you need is in the core books.
'Need' gets defined pretty charitably.

Consider the old-school stats on, well, just about anything. /LOTS/ was left very much up to the DM. I think as early as 2e, we started seeing all 6 stats for monsters, for instance. Some editions are more consistent in what they include vs leave out, is about all you could say on the matter.
As a published game, somebody who has never played before should be able to pick up the books and play ....
That's a bar D&D has never cleared without incident.

IMX, introducing people to the game from 1st through 5th ed, 4e actually presented the game in a way that was easiest for entirely new players to just pick up and play. For precisely the reasons it seemed so not-D&D to long-time fans.
An objection that [MENTION=87792]Neonchameleon[/MENTION] had about 3e stat blocks is that they cross referenced existing material.
Nod. Again, something that's present to varying degrees in all editions. 4e was the only ed that didn't reference spells in some stat blocks, for instance, and presented each & every attack, 'utility' & trait the monster had - yet you migth still have to cross-reference all the jargon used to present that so tidily.
So say you're not new to D&D, you're like me. What do I see in 4e design?
Something you're not accustomed to when looking at D&D. Yep. The learning curve was harder on old fans than potential new ones.
Perhaps I misread the intentions of 4e monsters and their design, particularly in the context of how the rules seem to be very combat oriented in general.
You did, yes, or rather, you read too much into it. They're monsters, they're statted as opponents in combat. The out-of-combat systems - rituals, skills & skill challenges, though more distinct from combat and more extensive than in other editions, didn't actually require a lot of detail on the 'opposition' side, as that was mostly handled by the DM setting DCs. (You might pull out a skill bonus or opposed skill check, out of combat, for instance, but the monster blocks did have those. FWIW.)
And, really, RPGs, particularly D&D, get that a lot. The rules /are/ heavily oriented on combat in general. It's a fact that underlies the erroneous conclusion that they're "violent games," as well, for another instance of people getting it wrong. Maybe it stood out for you more in the case of 4e because it didn't have the familiar presentation and structure of the classic game, the way 5e does, again?
That's the extent of the description. Nothing else, not even what they look like (presumably the assumption is that the picture takes care of that).
Yes. That was an overblown selling point of the MM books, that every monster had an illo.
Again, all I'm saying, is that I personally don't like the monster design approach in 4e.
It only takes one sentence to say that.

Clearly, it's not all you're saying. Either you're trying to convince everyone reading that they should dislike it, too, or you're trying to justify your dislike, when there's no need to justify a subjective feeling like that in the first place. In the process, you're making a lot of false and misleading statements and reaching a lot of erroneous conclusions. Prettymuch a typical edition war exchange, just without the implacable h4ter malice. (And thanks for that.)
It actually reminds me of early D&D approaches
Yes. The treatment of monsters was moving away from the mechanically-different-from-PCs, primarily-antagonist approach of the early game to a more detailed & mechanically unified approach that, ultimately, in 3e, gave virtually all the same options available to PCs to monsters and NPCs. 4e got back to the old approach, though with a very new & different presentation and mathematically robust mechanical underpinnings. 5e hasn't really pulled back from that, just reverted to somewhat more familiar presentation (it really didn't take much).
I'm not debating the merits, whether one is better than the other.
Maybe you don't intend to.
Overall I agree, but in AL adventures, or other organized play, I believe you pretty much have to stick to the monsters as written in terms of stats.
"In terms of stats?" Perhaps, of course, you can run a monster in such a way that, through rulings, those stats don't matter all that much.
I'm not certain if you can increase or decrease monster hp and damage in AL play (probably...)
Who'd stop you? Who'd even notice, really?
With something like a game system, an imperfect system that we all know how to play (and want to play) works better than one that the rest of the players have no interest in learning.
That's prettymuch the reason for D&D's success, right there. ;P Seriously, though, it's our beloved game, and the brilliance of 5e is in capturing the sense of D&D, as a whole across editions, well enough that we can all feel like we know how to play it.
Except that the offscreen stuff often works better with rules. For example, we have rules for researching spells, crafting magic items, etc. and these take a long time. How long is partially determined by the rules we have in place.
"partially?" Sounds like it doesn't always work better with rules.
Seriously, it depends on how you want to pace your game and what aspects of it you enjoy. One long-running campaign certain of my friends play in, for instance, is centered around the development of a town the party has more or less founded. It's like D&D Civilization. Two of the players are really deeply into it, and handle it away from the table, for the most part, though what they do has a big impact on what sort of challenges end up confronting the party. The rest of the group are just playing D&D more conventionally. The rules driving that off-screen stuff, though, aren't from any D&D source.
5e has downtime rules that can be used in place of actually playing out the scenes, if the players and DM determine that it's a better approach for that point in time.
I do like the idea of downtime rules, and would love to see 5e's fleshed out a bit more. They do impact pacing, though, so DMs need to keep in mind that they could always customize them, particularly simply changing the underlying unit of time to better fit campaign pacing, a useful tool that's also easily missed when it comes to the lengths of rests and the 6-8 encounter day controversies....
As for "flipping through the index" if you're familiar with the game it is a relatively trivial process to either know or look up what a spell does.
There's a lotta spells, for those of us with decades of familiarity, it's trivial. Though, when running 5e, I tend to run an NPC spell more or less like I remember it rather than look it up, so heavily colored by the glory days of 1e.
