From reading forums and whatnot, all I hear about is how this class is broken and how that spell is broken. I don't get it. Either people are extreme power gamers or they just don't appreciate the wonderful game that Wizards of the Coast designed for them.
My chief complaint is that WotC didn't provide as many examples of the special attacks of monsters as they should have, like the mechanics of negative levels. Or explain whether or not you can stack flaming on a magic weapon. On top of the ambiguity (which can be resolved at the table with house rules) is the constant stream of splat books that IMO added too much to the game and took the game away from the basics.