You could use the Nashville expansion to play any music, of course. It's a great sounding drumkit, with samples of sticks, brushes and fingers!
For rock and pop you would do well to concider 'the Classic' expansion. It provides 3 complete classic drumkits from the 70's and 80's
(Noble & Cooley, Yamaha, and Craviotto) and they sound awsome.
(No brushes here, but 3 full kits). The sound is very different from the standard GMS-kit. The GMS-kit is more agressive, more 'rock', while the 'classic' kits
(especially the Noble & Cooley) sound more acoustic and organic
(in my opinion anyway...).