In reading this thread while reading through and digesting my copies of the 4e rules - AbdulAlhazred's post here really helped me clarify some thoughts about the game.
I skipped the whole late 2e to 4e era and only played 5e for the first time this past year. I spent all that intervening time playing almost every other game not called D&D. I got the 4e rules as a reference to see what was done with the game. (And honestly to see what the whole fuss was about.)
So I really have zero emotional investment in what this or that edition of D&D did "better".
One thing that became clear to me was that in order to maximize what your PC class does: You must pay attention to how things work, and what is going on.
My impression - this codification drives a group to engage with the game in a very specific way to take advantage of everything in the rules.
It does not strike me as an edition of the game where you can really play fast and loose with the rules.
Or another way of putting it: The way the GM has to arbitrate more of the combat (And thus situational and environmental aspects are pure GM fiat) - players will naturally invest in attacks that are not as dependent on GM Fiat/specific environmental or situational conditions.
One thing I would say is that it is my impression that 4e drives players towards a more specific playstyle (i.e. Having to engage with the game rules in a more specific way) than other editions of the game due to the preciseness of its rules.
The preciseness of its rules also drives the need for more consistent knowledge of the rules from the group as a whole.
So I can easily see how a lot of D&D groups bounced off of this hard.
Especially groups that had players that engaged with the rules at different levels of 'mastery'.
Conversely if the style of game 4e delivered ticked your fun boxes in the right way: I can see how those who liked 4e - really liked it a lot. I can easily see how moving to what 5e does would be viewed as a big step back by 4e fans.
I do like some of the ideas I see in 4e, and I will do a one shot with it to see how it works in the wild.
But I also recognize that there is no way in hell 4e is a good fit for my group for a long term fantasy campaign. I have several players that will not engage with the rules enough to make it sing like it should.
Here's the thing about 4e IN GENERAL. The thread opener was a question about what makes 4e a 'tactical' game; so I focused on answering that question. 4e is however, an incredibly flexible game! It is, IMHO, a Story Game; that is, its intent is to be focused on the story and for the action and process of play to focus on story, and particularly to give the players a bit more of a role in it than they do in a traditional D&D game by default. Players are pretty much in charge of how their character is built and have very many options to choose from during build (4e also offloads a LOT of work onto build time, you don't actually NEED huge 'runtime' game mastery to play 4e, no more than other editions, probably less in many cases).
It suggests that GMs consider player's preferences when giving out treasure, and it assumes that the GM will grant items within certain categories (later rules make that less of a concern). Players are granted the right (although the DMG hedges a bit) to define QUESTS, which are the fundamental story driving framework of 4e. And then both combat and noncombat action adjudication is much less A) built around GM adjudication, and B) much more structured. This means that when a player in a 4e game decides to have her character take some risk to perform an extraordinary action that the 'valence' of that move is apparent. If its part of an SC, then the outcome will have a mechanically defined incremental input into the overall success or failure of the SC (which is basically an encounter, though it could be more extended narratively). The same in combat, the 'tactical' nature is there to give the players assurance that if they unleash "Big Impressive Daily Power" that the range of potential outcomes is cognizable.
What NONE of this does is impose restrictions or imply that the game isn't as able to handle 'winging it' as any other D&D, or other RPGs generally. It is. There is a very tightly defined set of keywords and interactions (and you can think of things like class, race, origin, power source, etc. as effectively keywords, though that isn't really stated). You can leverage this. You would find
@pemerton's descriptions of 4e play in his campaign to be quite interesting here. I have experienced similar types of play to what he describes. It is very dynamic, very open-ended, driven heavily by player choices, and allows for a lot of 'stuff to happen', and seems to be perfectly in keeping with the 4e rules, though not everyone is in agreement that WotC was intending this form of play (but hey, they say 5e is for everyone, I say 4e is too!).
So, you see things happening in games like "I break the Holy Avenger on him." Hmmm, that's very interesting, definitely an improvised move! Lets see, this thing is a demon lord, and the sword was FORGED TO DEFEAT HIM, what do you think happens? I mean, this would be the ultimate move of some SC, or the pivotal move in some combat. So, something pretty amazing happens now. There's no RULE for what that is, or why, or how, it has to be (well how can leverage all the excellent rules) but that's the point, the game doesn't tell you what to do, ONLY how it could be done, just like every other version of D&D in the past!
I'd also say that 4e DOES strongly favor certain styles of play in terms of what kinds of combats, for example, work really well. The game is not good for and useful to run trivial encounters. Its not a world simulator, its an ACTION GAME. If you are slogging through rooms full of dull and mundane seeming foes, then something is wrong! The DMG says it pretty plainly SKIP TO THE ACTION. Don't dwell on skirmishing with gate guards, get to the throne room. That other stuff can be significant, as a pass/fail check on an SC that helps decide how many guards are in that throne room, etc. It is just a waste to run 12 fairly trivial combats. Run the one where the Grand Duke shows up and reveals he's really a Devil, and then the one where the Captain of the Guard, whom you got on with well, apologetically lays onto you because its his duty to die for the king. Do the finale, make the rest color or SC fodder. Every combat should be dramatic, filled with personality, happening in a dynamic environment that itself is a participant in the fight, and evolves as it goes on. If Steven Spielberg wouldn't film it and put it in an action movie, it will probably not be that great of a fight.
4e is not your dad's D&D, but it is still D&D, and it can be a REALLY good game when it is played to its strengths. It can do more classic D&D adventures OK, but honestly its not the reason to play it.