Apparently Guitar Hero 4 will be worth getting.
http://www.escapistmagazine.com/news/view/83840-Guitar-Hero-4-Adds-Drums-Create-a-Song
So yeah, looks like I'm going to have to get GH4. The ability to upload your own songs and make your own guitar, bass, and drum note charts is a biggie. Also, the game is going to have The Eagles. Not that it would really be an issue, cause of the whole adding your own songs thing, but yay! Also, the drums look to be more interesting and more robust than their Rock Band counterparts.