Dream Theater really aren't diverse at all.
In fact, diversity really isn't a calling card of metal to be honest. But in saying that, I don't want diversity in Reign In Blood, I want an unrelenting aural skull fuck assault or some other such stupidly descriptive phrase. Sure, metal has some contrast, but hardly much diversity - it still keeps coming back to a central sound pallette.
Good call by Slunk on Mellon Collie..., that album had so many differring styles on it that it was constantly described as 'unfocused' and 'self-indulgent' by the press when it was released.