In my mind, unquestionably yes. It really has done. You use the example of the PHB, but while there is stuff in there that was absurd broken or outright awful, there was so much good. We had one of the first non-cleric healer classes in 4E ever that was awesome (and still is) in the Warlord. We had fighters that weren't simply fodder and wizards/clerics were not gods. The game has expanded a lot since then adding in numerous other elements, with some pure crap (Beastmaster Rangers) but there was always gold to go with it (Like the brawler fighter).
Well, I think Beastmaster Rangers kick ass

, but yup, there's gold AND THERE'S STUFF THAT ISN'T. In EVERY book.
Like let's consider one of the most monumental and important books in terms for DMs last year: Monster Manual 3. There are 303 creatures in that book. There are seventy four monsters over level 21 in that book. That is just fantastic, because many of them aren't even elites and solos - plenty of good old fashioned standard monsters (albeit with awesome epic tier powers and tricks!). I have never said a bad word about this book just about ever
Let's look at the essentials monster vault. There are twelve monsters over level 21, out of three hundred and four monsters. Now that's just bad. This is an excellent book with fantastically designed monsters, yet it was immensely disappointing because of what it didn't include. Not even ancient dragons for gods sake - something that is iconic to the game. I can forgive it for this because I thought "Oh well next book will offer something and - " oh wait. The next book ALSO is ditching epic tier support again (as the book is explicitly for heroic and paragon tier). So once more something I should be excited for I am barely interested in. Despite the fact the preview was unequivocally awesome.
So MV and MV2 are horribly flawed because they weren't aimed at the specific aspect of play that you're interested in seeing more support for? Lets look at MV, it has awesome monsters in it, like the new versions of the dragons. It was aimed at being a generally useful book for all players, and specifically for starting players. Low level monsters NEEDED BADLY to have another look. I realize it didn't focus on what you would have liked it to focus on, but you know that happens. Not every book focuses on what I specifically want to see next either. Calling it 'bad' is just not warranted.
How should that be possible? To have such a fantastic preview and yet not get me remotely excited about a DMs book full of great monsters? Oh, I know why - because it completely ditches an entire tier of the game well supported in every previous monster book. Thanks Wizards.
I thank wizards profusely for MV. I've found a vast number of excellent monsters in that book which I have been very happy to have and use eagerly and with pleasure. I'm not discounting anyone else's tastes. The fact is if you are publishing a game system you simply have hard choices to make. Every epic monster in that book means a heroic tier monster or a paragon monster that has to be dropped on the cutting room floor. Consider that. Take a balanced perspective.
Now let's consider Heroes of Shadow. I thought this book should have been great support for necrotic as a damage type. It added a mediocre striker class onto the pile of mediocre classes (Vampire - making it almost entirely devoid of options and on rails to add insult to injury), it added a decent striker in the Blackguard (who is pretty decent at what he does), one of the worst possible options in 4E in the Binder (who is worse in every way to a regular Warlock) and more options for wizards/clerics (who were SO lacking in them obviously). It did nothing for necrotic in terms of feat support, which is still a terrible damage type and added a bunch of feat cruft that nobody will ever take. Oh and reintroduced the concept of racial penalties into 4E: An awful design decision. So unlike previous books, I can certainly say there was way more bad than there was good in this - probably for the first time this edition.
And I disagree. IMHO you're too caught up in mechanics. You've become far too focused on dice and numbers and your vision of the game has become too narrow. By simply making an "avoid necrotic resistance" feat or two (or whatever the exact mechanics would be) simply moves necrotic resistance from something different, interesting, SCARY, into just another damage type exactly like all the other damage types. Vampire is an awesome class because it depicts a vampire quite well. I've said it before and I will say it again.
Mechanics which fail to provide any kind of CONCEPT which gives us the ability to do something genuinely new is worthless. I can say the same about most of the other material in HoS. HoS particularly of all books requires strong theme. I haven't spent much time analyzing the Binder, but I can tell you that the class works, and in fact IMHO provides a more thematically coherent warlock (albeit a somewhat narrowly defined one, I wouldn't want that to be the ONLY warlock). There are already a vast number of different mechanical options out there. An HoS which simply provided more of the same with different adjectives attached to it would have been a waste of ink. I can already refluff things myself. HoS succeeded well in its purpose, giving us options that play in genuinely new ways and open up thematic concepts which were not available before.
Then we get these themes. Now last year I remember being nothing but excited about Dark Sun. I devoured all information on the setting I could find and of everything I read, themes were the things I was most interested in. Mostly because I wondered if they would turn out really badly or not. As it was, I think themes were one of the best things added to 4E. I loved the concept and the mechanical effect was reasonably limited. Some exceptions, like most things in 4E exist. Like rangers whoring the 18-20 crit range of the Wilder theme with twin strike + interrupt attacks. Noble Adept was arguably one of the strongest themes as well, with its leader interrupt power that can apply to any roll. In general, they really hit the mark and successfully. There is no theme I can say is outright awful.
Now we get these themes. Gutted and stripped down versions of the originals. I can say that the animal master is outright awful, one is frankly superior to any theme I can think of (even noble adept from DS won't compare to getting an entire classes awesome utility powers), another asks major questions about rules loopholes (getting the item and training it out - what happens to the item?) and another is actually okay (checking LFR, they have ruled that all alchemical items are common unless otherwise stated. I didn't know that, but it's a ruling I'm putting in my own games as well). I mean in terms of being thought out I just don't see the degree of balance and design in these compared to the DS themes whatsoever.
And again, in the case of Order Adept, we agree. As when they designed Twin Strike, Rain of Blows, Blood Mage, etc etc etc they got one out of four a bit wrong. No doubt it will have to get hit with the nerf hammer, but what is that going to take? A 2 sentence errata? Ouch, that is so terrible. I will repeat what I've said before on the subject of the other themes:
1) It is not necessary nor particularly advantageous for WotC to mindlessly repeat the same formula they've used before. DS and 4e in general have slightly different goals and requirements. The new themes serve a slightly different purpose from DS themes and have to work with different character types and needed to be slightly different.
2) AGAIN, CONCEPT TRUMPS MECHANICS. This is a NECESSITY. I cannot repeat this enough times. An Animal Master mutilated into something that fits a highly rigid power structure at the expense of any kind of thematic appropriateness IS WORTHLESS. There is no point in putting out material that doesn't give people options that are worthwhile character development concepts. This is especially true at this later point in the 4e product lifecycle where people ALREADY have a vast array of mechanical choices and the main complaint about the game is thematic, not mechanical.
Corner cases like Neonchameleon bought up with an avenger ranger (which isn't actually possible by default in DS, but some DMs DO allow divine options so is worth considering) do happen with DS themes. But there are some major imbalances that occur among a whole crapload of classes with one of these themes. Any defender would want shield. Any defender would like wizards escape. Any defender could use flight for an entire encounter + insubstantial (one of the later utility powers). Hell who couldn't use shield? Wizards escape? I can't think of any class that wouldn't mind having an ENTIRE classes utility powers to choose from, on top of getting +2 will and other benefits. The irony that Wizards get the least out of a theme that apparently suits them by fluff is just the icing on the cake here.
And we agree on this point. My issue here is you're condemnation applies equally to every single 4e product released by WotC. The issue isn't WotC, IMHO you want to look closer to home. I really don't mean that to sound harsh, I've always appreciated your voice here. I think the super critical Aegeri that cannot be pleased though is not the voice I was enjoying. Call me selfish, I'd like to see that version of Aegeri more than the one I'm hearing here now. I realize I'm projecting my wants and desires on you. As I said, call me selfish, lol.
In a long winded way, I do think quality is going down. Both in the range of options available - even in the really well designed monster vault products that completely decide that epic tier is no longer worth supporting. We are filling books with fluff and reducing meaningful crunch options. Anyone should have been able to point out obvious problems with some of these things before publication: The shades racial power. The order adepts ridiculous benefits compared to the three other themes presented. The binder being pretty much worthless in every conceivable way. Dragon is just laughable really compared to what it was - I mean do you have an argument to even offer against that statement?
Sure, my argument is the same one I've been making during this whole thread. This is not some kind of new phenomenon. You're going to tell me that Student of Caiphon was just fine? It wasn't obvious it would be poached? It was obvious to ME when I read it (and sure enough I had a player do that too). I won't belabor you with the vast number of examples. You know the material as well as I do and, again IMHO, I think the issue here is you've gone from focusing on what is fun and interesting to what is imperfect or doesn't satisfy specific itches.
Quite frankly, I do believe the quality of the games design is going downhill now. Like there were always stupid things before essentials, but they were always put right alongside the damn GOOD things. Now we have the stupid things and none of the good things. That's the problem.
I don't design this game. I just devote much of my free time to running 2 games that I vastly enjoy every week (adding a third soon I hope!). I wouldn't mind Wizards feeling like releasing epic monsters and a working monster builder at minimum was something worth doing. But that's just me. I mean, this is it now for me: I've bought ALL my expectations back to those two things. If Wizards can release some epic monsters (or adventures, as they've promised) in future and a monster builder that builds monsters, I will call it even.
Is that so unreasonable to you? Is it unreasonable to anyone?
Eh, it isn't a matter of reasonable and unreasonable. It is a matter of outlook. I perceive that the outlook of some people has changed. I don't think the quality of the game system has actually changed. I think the designers have come to a point where they've said the big things they were after saying with the game as it was released in 2008. I think the aims they have now involve gaining a greater understanding of and emphasizing more the territory they were accused of abandoning with core 4e. This could be looked at as pandering to critics of the game, but it can also be looked at as a purely natural evolution. Mike Mearls and Co have pumped out basically every combat option that anyone will ever need, rehashed them, and rehashed them again. The newer material is more thematically oriented. It is the designers saying "yeah, and we can also have a class that sticks to its theme even if it won't appeal to some min/maxer." The game grew up.
Honestly, we come from very different perspectives (at least so I gather). I've LONG ago been through my gaming phase where I craved new tricky mechanical stuff for its own sake. I've LONG since been down the optimizing and power gaming road, and back. I've done all that stuff. All I care about now is having a good variety of material, solid mechanics, and support for cool concepts that can be folded into my game and I don't have to invent for myself. Something like Vampire is perfect. The distinction between necrotic and elemental damage types is perfect. A Binder that manifests bound spirits is great. I eat this stuff up. I'm OK with someone saying "Oh, there's this mechanical problem, doing X instead of Y could solve this without breaking the concept." That's great, and I don't have an issue with that level of critique. I do have an issue with the idea that what we had 3 years ago (which often did NOT support many of my needs thematically) was superior to what we're getting now. It was different. It had a different emphasis. It was good stuff, but what we get now is good stuff too, better in some ways.
Anyway, peace. Just think about it.