Dream Theater

Dream Theater are a good band. We can't even describe their genre.
Progressive rock/metal? Yes, but with more piano.
Alternative metal? Certainly.
Extreme metal? In case you're envisioning something like a bizarre hybrid of death, black and thrash metal. NO!
Although some bits do sound like Metallica. You'll even find little bits of sounds reminiscent of bands like Korn and Slipknot. No, that does not make them nu-metal either. Like is was mentioned before: we can't even describe their friggin' genre!

Songs

It's called 'Dream Theater' because they can play songs in their sleep. Like Metropolis, Pt. 1. They know that one so well. THE BOTH OF YOU, WILL BE CONFINED, TO THIS TIC TAC BOX...
Wait, did I go off track?

Albums

Very astonishing.