I finally had my first session of 4e tonight. We didn't get far, most of it was the team learning how to put together 4e rules, but I can safely say I'm hooked.
It's so good now. The game mechanics are very bizarre, very abstract, and don't make much sense in real-world application. You can make attacks that utilize Charisma instead of Strength, and cause status effects, as a paladin. Why? Because it's magic. They don't make sense if you think about it at all, but if you step outside of the 3e mindset it's totally great.
Sure, WOTC has put a blanket-ban on all powergaming and Red Mage-ing your character. You don't roll hit points anymore. Stats all go up constantly throughout a campaign instead of just a few times. There's no freedom-of-manipulation spells anymore. Magic Missile requires an attack roll. There are hardly any illusions. Gnomes and half-orcs are gone. Multiclassing is very very specific and not nearly as powerful as it used to be. The system enforces using rogue backstab and abilities only with Rogue proficiency weapons.
But, I mean, who really cares? 3E was broken to hell. Ranger was level one, and MAYBE level one through five. Fighter and wizard were the best classes. Not multiclassing hurt your character immensely. Prestige classes were vital. Fighters were usually horribly boring to play. Clerics were impossible to have any fun with, as every spell ended up getting dumped for spontaneous healing. Wizards were the best class period, and able to handle any situation with the right spell. 3e practically praised continually playing the same character into epic levels, instead of just knowing that, at one point, your character's campaign is over and he's made his claim as an adventurer.
4e fixes all that. Each class does fun things. Rangers are the only ones whom can dual-wield at will, and multiclassing them takes 11 levels and several feats before you can use both attacks. Everyone else gets the choice of which weapon to attack with and gets bonuses for two weapons depending on a feat. Fighters are tanks and melee destroyers. Rangers are distance bowmen or close-range damage machines. Wizards are nukers and controllers. Clerics have abilities to heal and deal damage simultaneously, thus removing the awful "Healbot" status. Rogues are damage machines and combat manipulators. Everyone has several abilities at once, including per-encounter powers and once-a-day supermoves. Even without this, casters have Rituals, giving them more capabilities of casting beyond mid-combat.
4e is everything I wanted in a DND game. Even better, as a DM, it's simple as hell to run. Instead of the complicated CR system, you just have an XP budget and purchase monsters from them, and they encounter each set of monsters one-at-a-time.
I love fourth edition and it's so incredibly wonderful. I heartily endorse it.