When playing Rock Band, I notice that the songs I have the most fun playing my guitar on are normally the songs that make you move your fingers a lot, without being a heavy-overkill of notes. So I guess I like hard songs that aren't TOO hard, but have a nice challenge to them. What do you like in a song chart?
If there's any types of note-charts I can not stand, it's the ones that make you hammer the same note for the entire song. I notice that more in Guitar Hero than Rock Band, though.