Some bands might be good, some might be bad, but this one is definitely one of the best ever. To call it unique is to say nothing about the maturity of their style, complexity and intellectual quality of their lyrics. There are much more so read on.
Hard rock would be the closest style category, but their music is always so different that I don't dare dumping them in just one category. There are songs that are pure metal, slower rock and others which are so insane that they require a different style of itself. They are not afraid to say what has happened and what is happening (Armenian genocide is one example).
One last word:
Their new album called Hypnotize can definitely stand by the ultimate classics of theirs like "Chop Suey" and "Toxicity".