First: I agree with Henry, overall. he summed it up, almost perfectly.
Second: For the first time I can recall, I fully agree with Thasmodius.

regarding character building, at least - I definitely prefer creating characters in 4e over 3e, and I wish there were fewer feats. Too much choice is a bad thing!
Now, that out of the way.
People saying that all games are mechanically homogenous have never played, say, Shadowrun. The rules and sub-rules for creating a decker were entirely different than that required to play a rigger. Every character had to be built in a completely different way, and followed different rules systems... sure, while character creation followed the same rules, each "class" had a different emphasis in character creation.... Deckers and Riggers tended to require a lot of starting money (for cyberware and programs), while stealth-based characters required attributes, mages required a lot of spell points, and so on.
Now, I have argued since this game came out that it is homogenous outside of combat - that a fighter isn't much different from a rogue outside of a fight in mechanical terms (yeah, they may have slightly different skill choices, but with backgrounds, even that isn't necessarily true). Some say this is a good thing, some say it is a bad thing. I'm not entirely sure either way, myself. But that, to me, is a fact. Unless you count in things like rituals and magical items (and what 1st level PC starts with magical items? And how much player choice is involved in a PC's magical items depends on the individual GM). Outside of a fight, our Halfling Rogue and our Drow Rogue are almost mechanically better. The dragonborn paladin and the eladrin warlord. And so on.
As for IN a fight... I'd say yes and no. I think the roles are mechanically similar - defenders are up close and take hits, for the most part. Leaders heal their friends and grant bonuses. Controllers dish out status effects. Strikers deal damage. They are fairly similar, though KM makes a good point that the last two roles are a bit more varied in their approach.
That being said, there are pretty big variances there, as well. A Paladin is a very different defender from a fighter - I see it every monday when we game. We have a dragonborn paladin and a minotaur fighter. The minotaur often pins down one big guy by himself or pairs up with a rogue, taking the hits while the rogue deals out the damage... or he'll go for the super mobile guy and keep him pinned down in melee combat. The Dragonborn, meanwhile, sticks with his allies, and marks an enemy while using powers that improve upon his allies' defences, or makes an area a better combat zone. So, the dragonborn becomes a solid front line/centre of a shield wall, while the minotaur is much more of a skirmisher.
My biggest issue with 4e is not homogeneity. I can live with it, because I can create the characters I envision in my head (especially now that I can use hybrid rules!). And the fact that things are homogenous make it easier to create adventures and encounters, which is a HUGE plus.
My big problem with 4e is the economic system, the focus on gamism as opposed to simulation, treasure packets, and all that fun stuff. Luckily, when DARK SUN comes along, I'm going through the trouble to get rid of all of that. Then 4e will be almost perfect.
