It's good fun, looks great and the voice dialog couldn't be any better (especially for the Heavy: "You are a good doctor!"), however... some things that make me want to
1.) no grenades. I can see the argument that they lead to grenade spam near spawns, but c'mon, there has to be a better solution to that problem other then removing grenades altogether!
2.) no armor. In previous versions of Team Fortress there were Health and Armor counts. The medic healed you if you got wounded and the Engineer fixed your armor. It really did add a lot to playing as the engineer when you could fix up your team (speaking of the engineer, he's also missing his railgun...).
3. still on Engineer) destroying your buildings doesn't kill any nearby enemies (so far as I can tell). One of the great tactics of past Team Fortress games was to build a dispenser in some heavy traffic area just around a corner or something, fill it up (which you also can't do in TF2), and then use it as a remotely controlled bomb to kill any enemies that passed by.
4.) there are only 6 maps in the initial release, which is fine and all, but only one of them is a classic Capture the Flag style. The other 5 are Capture Point (CP) maps which I, personally, find less enjoyable.
I think once the novelty of the art style wears off (don't get me wrong, it truly is fanstastic), people familiar with the earlier versions are going to start realizing that TF2 is actually less a game than either TFC or TF were. They removed too much and added too little in return. Really, where's the stuff that makes this "Team Fortress
2", right now it's basically just Team Fortress:Source with stuff missing.