I can of see the complaint that all the classes are more or less the same in 4e, but only partially. They all operate under the same mechanics, once you get how to work one character, you won't have to much trouble trying out the other characters. For myself personally, I don't like this. I like crunch, and 4e takes out a lot of the crunch.
As I said before, and others have, 4e is shallow of a game, and pigeon holds you terribly. However, that is the goal of 4e, and I think it does it quite nicely. The class, though operating similarly affect each other and their challenges in different manners that encourage fast decision making (as in faster turn pace for combat), and team work. Team work, I think is much easier in 4e then in previous editions.
I appreciate that the classes aren't broken. The spell casters have been spoken to in length for their over power spelled, but most classes had various issues. Rogue, my favored class, I think even without the additional errata from misc. rules books that its the second class pose for the most abuse.
Rangers, are broken in 3e. It gets better in 3.5, but its still a wonky and weird. The same goes toward the Paladin. The Cleric, couldn't perform its party function when it was low leveled. Bards were so aimless in their ability, that it was hard to use them. The Fighter and the Barbarian in my opinion are the only two well design core classes in 3e.