It's been a while since the release of 4th Edition, long enough for me to finally get a good sense of the game.
There are many things I like. Many of the 3.5 problems or annoyances have been dealt with, such as ponderous grappling rules, uneven character classes, race blandness, overlong stat blocks, the "christmas tree" magic item effect, and the dreaded amount of math that goes into monster building and leveling. Sometimes for me, it's the simple things—like diagonal movement. The 1-2-1-2 rule wasn't hard to remember, but I didn't DM a single game wherein I didn't have to remind a player of it. Attacks of opportunity was another one that tripped up my players, and nothing irks a player like being told their PC got nailed when then thought him safe.
Many folks online have commented that the "soul" of D&D seems missing from 4 however, and I sadly must agree. I feel that way too ... but why? I've puzzled over this for a while now. Here are the reasons why I think my gut tells me I'm just not playing D&D (when playing 4e) anymore:
1. The death of too many sacred cows. Magic missiles that miss? No more vancian magic?
2. Too much player information/involvement. No, I don't believe in that "I'm the all-powerful DM" attitude, but there's a line. Putting magic items in the Player's Handbook crossed that line for me. Magic items should be fairly rare and wondrous, mysterious, and even potentially dangerous. Reducing them to a shopping list and asking players to create wish lists? Meh. (What's next, an Amazon-like website that suggests to players magic items their PCs might enjoy?) There's nothing wrong with a player conveying that she dreams of playing a mighty fighter with a magic sword or a wizard wielding a mighty staff, and the DM trying to oblige. DMs should try to please their players and let them live out dreams through their characters within the balance of the game. But wish lists? I say thee nay.
3. Forced monster organization. As a professional adventure author, I can tell you that 4e's monster system is a pain. The "let's set up groups of mixed creatures" can indeed make for interesting combats (never a bad thing), but the system makes it near impossible to create combat situations in which the PC meet a group of one type of creature (which need happen fairly often for realism's sake) or a single creature that isn't a solo. Do you want to have the characters in the sewers run into that random alligator? Forget it, the combat would be over in a second; best make it two alligators, one shambling mound, and eight stirges—never mind that those creatures would never realistically hang out together. (Some of the monster groups presented in the Monster Manuals are good for a hoot too.)
4. PCs are too strong. As a player I find rolling up new characters mid-adventure to be a pain, and I'm a notorious softie as a DM when it comes to killing off player characters, yet I do feel low-level PCs need to be vulnerable. That sense of vulnerability only leads to a greater sense of accomplishment later when the PCs level up.
5. Nostalgia. That sense of wonder is largely gone. I honestly blame this more on my gaming longevity than any game edition.
6. It's all about combat. I love destructive spells. Love 'em. When playing a 1st Edition wizard, I long to hit 5th level so I can add fireball or lightning bolt to my spellbook. But there are other things. The heavy combat slant of 4e's powers and spells can reduce handy roleplaying opportunities that can stem from using a certain spell in just the right way, etc. Roleplaying opportunities still exist of course, but the previous editions had spells or proficiencies that screamed for a dose of roleplaying every time they were used, and I miss those.
7. Excessive DM hand-holding. Ultimately any DM guideline is just that. Former versions of the game and even some hallowed modules—Village of Hommlet I'm looking at you—had some extremely lop-sided treasures. Either the players got crumbs of they were tossed necklaces worth 10,000 gp. But the parcel system breaks things up a bit too neatly, eliminating the DM's freedom, and player awareness of that system places unfair expectations on the DM.
Some of my reaction to 4e (and a lesser extent 3e/3.5e) is that of mixed blessings. I've always been a big miniatures user, and I've suffered from players (and DMs) "stretching the limits" of how far figures can move in a melee round, etc., so having a more miniature-oriented game was a blessing ... at first. Now I'm not so sure.
Likewise with feats and later powers. I always thought fighters should have a selection of cool moves to select from, but now it's started to leave me feeling flat. The ever-expanding list of powers has become like MAGIC cards (which probably makes sense given the company involved) ... more and more minor variations of the same stuff, with power gamers examining every detail to wring out the stronger options. I realize many find this system tinkering fun, a puzzle-like quest to optimize their characters, but to me the more time a player delves in the rules the less time they're actually involved in the play itself. The hyper-awareness of the rules that 3.5e bred by "rulifying" every aspect of the game extends to 4e, and as a player I don't want the rules in my face every second, I want to lose myself in the action. To some, the statements "I swing from the chandelier and strike out at the orc with my feet, knocking him back if I can!" and "I use my daily Juggernaut's Roll power to push the orc two squares east!" may be the same thing, but not to me.
Ultimately the soul of a game is in the play. Rules can be modified, play can be altered, and both DMs and players can tweak any system to find what works best for them. Does 4e as written have enough "soul" for you?