Even during 3.X I was already starting to lean away from crunch heavy games and was looking for something else.
4E was the most amazing edition for me, but yeah, there's no denying it was almost as crunch-heavy as 3.XE (individual players had a lot less to know/remember, at least, because of the structural changes to the rules), and it was the sheer amount of crunch, particularly at high levels, that eventually steered me to Dungeon World (to be fair I also completely adored the concept of DW - sadly only three out of five players "got" DW, the other two were endlessly perplexed by certain elements).
Paradoxically, the end result was that it became too much of a wargame. Players were constantly arguing on which order to trigger powers, wanted to change powers at end or beginning of each session because they felt they had made a suboptimal choice. The creature stat blocks were getting longer. I felt I was playing a wargame against four other opponents.
I was increasingly tired at the end of each session as they gained levels. At first thought I was getting too old to DM. I never felt that before. I decided to play other rpgs and I didn't feel the same level of fatigue as with 4e D&D. I stopped playing D&D.
The publishing schedule was on steroids and far too segmented. Too much of a chase grab by Hasbro for my taste. I used to opportunity to read and play other rpgs I had collecting dust on the shelves. I played less often but had more fun.
These seem pretty legit criticisms to me. I never saw the tiredness myself, indeed I was always pumped at the end of the session, and my players weren't arguing, but rather trying to cooperating in increasingly elaborate strategies (which only got more complicated with the Shaman arrived and was constantly triggering out-of-turn attacks and so on), but I can definitely see where you are coming from.
And I loved the release schedule, but I loved it because of the DDI, and the fact that as long as I stayed subbed I got literally all the rules, from all the books, in a really good format. Still, it was definitely intense! I don't think I'd go back without a solution to the interrupt/immediate action/reaction problem. That can probably be solved just by banning a bunch of powers, or having PCs have to run any powers they pick past me, but it is a real issue.
Back on to good points of 4E, can we talk about how totally awesome a lot of the 4E classes were?
Bards were amazing. They weren't as powerful as 5E Bards (hilariously, the 5E Bard is like what my 2E Bard, in wildest dreams, wished to be), but they were REALLY Bard-y, with their whole own deal that worked really well.
Rogues... Rogues in 4E were total bastards. Murderous, terrifying individuals. The astonishing, and yeah I admit, video-game-esque stuff they could pull off, was staggeringly cool.
Fighters were total lockdown murder-machines. We have a Battlerage Vigor Fighter, and he was virtually unkillable, and really violent, and messed anyone who tried to hurt his friends.
Clerics actually got to use their non-healing spells, and had some had some amazing control and denial abilities. Not as big an upgrade as some classes, but our "always ends up as the healer" player appreciated it.
Avengers - Nothing like them in any other edition. Terrifying constantly teleporting two-hander wielding killers who could pull off incredible badguy assassinations. The 5E Paladin subclass is cute but it's not even a shadow of these wonders.
The Psionic classes - probably the best implementation of Psionics for the rules of a given edition. Battlemind was my personal favourite, extremely well-designed, powerful but different from other Defenders.
Warden - Ahhhh yes, another unmatched in other editions, a weird and wonderful combination of partial shapeshifting, druid-style combat magic, and a tremendous primal vibe.
Swordmage - A wonderful Fighter-Mage-style class that really felt like it's own thing, and just really well-realized in way you rarely see.
Vampire - Actually a class in a main official book, finally, after first being a class in one of Gygax' early D&D games (the Cleric was originally invented to counter the player who was playing the Vampire), and they worked really well. I thought it was a dumb idea when I heard it, but they nailed it.
And so many more. What was really amazing was that virtually all of them played decently, and weren't innately overpowered/broken (usually you had to MC to break them). Given how many classes they made, how fast, and how complex some of them were, it is a truly astonishing feat of balancing that they were as good as they were.
(People may be saying "What about the Warlord?" - I wasn't a huge fan - it was a good class, with some wonderful applications, and filled a hole that's still present in 5E, and was obviously a hole in 3E too, but I felt like there were elements to the design that ended up making it too much of a straight up "buff the other characters" class.)