Guitar Hero Aerosmith is very much what I thought it would be - GH3 with a strong flavoring of all things Aerosmith. This isn't necessarily a bad though though. While the game lacks the difficulty of GH3 in the expert difficulty, you'll still have a good time playing it. If you're not a fan of Aerosmith, but still enjoy Guitar Hero - this game is a great rental. While I didn't enjoy all the songs, I did enjoy a lot of them, and it was just enough and not too much Aerosmith. With around 40 songs there is enough to keep you going for a while as well.
My only problem was that it lacked the difficulty that GH3 had in the last 2 sets. As I've played each GH game I've improved and I enjoy a tough challenge. There weren't ANY songs in this game that were anywhere near as difficult as other songs in the GH franchise. That being said - if you play the game for the fun and not necessarily for the challenge - this game is right up your alley.
This game serves its purpose to keep us hooked on Guitar Hero until GH: World Tour comes out.