I think they're the most realistic instrument - for example, really good guitar players often can't just start playing GH on expert, but really good drum players are often a lot better at drums on Rock Band and whatnot.
I'm mostly a guitar guy, but since I realize I'll never beat Dragonforce (and for me, that's really the final frontier...) I've started on drums. Which are much harder than guitar sometimes. My right leg muscle is getting a lot more built up than my left...