Read the books, played the game... I am not wild about 4E, though may play one-shots when I need time to work on my 3E campaign.
The classes, at least for my group, did play like a big gumbo, with none really distinguishing themself from the other. One woman played two characters last night (to insure all the "party roles" were filled"). She was a cleric and a paladin. Nobody noticed that half-way through the night she accidentally switched the sheets with her powers for each class. There wasn't enough difference between them. As a test, my son made "Power Cards" for the cleric, the rogue and the warrior today. He left out any flavor text, and the power source. Instead of 2(w), he put 2d6 or whatever fit. Mixed them together. We couldn't put them to rights except that he had put the names of the powers on the back.
The complexity of combat seems to be constantly overlooked. Does somebody have a spreadsheet or something I can take a loot at for keeping track of which effects are on which combatant until they make which saving throw? It ended up causing arguements and detracting from any fun we might have had. Because unless each PC is limited to using one such power per encounter, it just becomes sloppy. That plus the constant movement (shifting, sliding, etc) and over dependence on exact positioning are more mood breakers. Where we used to roll a few dice, maybe use a feat, and then I gave a good graphic description of what happened ("You swung your sword with such power that you cut the into the zombie with a sickening squelch and hewed the entire left side of his abodomen from his body, with decomposing entrails splashing to the ground."), we are now worrying about a dozen game mechanic worries and by the time damage is done, the illusion has been broken and it becomes "You hit the zombie for 5 HP.".
The people I play with feel extremely constrained by even the idea that they are supposed to fill specific roles. They want to be allowed to be more original than the two-dimensional straitjacket of "controller, defense, leader, DPS" (Ooops - DPS is for MMO's - I don't remember the term they use in 4E right off the top of my head.) It's not even that they necessarily have to be constrained - it's that they feel that they are required to be constrained.
The Wizard, who always plays a wizard, did like the love 4E gave him. I don't know what all the noise has been about, but I have never played in a game where a wizard could hold his own in combat. All of a sudden, a first level wizard was kicking behinds! No more resorting to a cross-bow. Though he did start referring to Magic Missile as his new crossbow. And he misses a lot of his old favorite tactics - casting silence on an enemy caster, knock on an enemy fighter's pants, and using tensers floating disk to just generally float around annoying the other side. - he's a joker and likes to do unexpected things. Plus, no familiar - no live animals for anybody - no animal companion for the ranger or mount for the paladin (though she isn't high enough for one yet, anyway).
By the end of the third game session under 4E, they were all begging to go back to the "older" version. (Using Pathfinder rules.) Next session - we will play half 3E if they will give 4E one more chance. (I paid for the books, I want to use them.)
Eric