While some won't like the direction Activision is taking with Guitar Hero, Guitar Hero Aerosmith is a solid game.
Lets get one thing out of the way, GH:A is Guitar Hero and you can't really change that. It is pretty much an expansion pack to Guitar Hero III being that it has many of the same features and plays the same way. If you're looking just to get a new Guitar Hero fix, check here because that is what you'll find. But for anyone else, there isn't really anything new to warrant a purchase here unless you're a huge Aerosmith fan.
While the game's set list isn't completely Aerosmith, it's not a lot of fun to play a Guitar Hero game based off of one band. After a little while you'll want some variety. The good thing about Guitar Hero 1-3 is that there was a ton of variety. That being said, playing songs like "Dream On," "Sweet Emotion," and "Walk this Way (ft. Run DMC)" are very fun, but you have to wonder why songs like "Crazy" and "I Don't Wanna Miss a Thing" got left out.
A few miscellaneous improvements are very aesthetic. The animation and mocap have been improved a little bit, but only one models of the band and DMC, when you're playing other songs with the Guitar Hero characters, the animations are as stiff as ever, and don't compare to the likes of Rock Band. The achievements in this version are far more attainable than those of Guitar Hero III, but other than that, there are no other real improvements.
When it comes down to it, it's just Guitar Hero. And the fact that we're at a point where we can say "it's JUST Guitar Hero" is a bit disconcerting. But like I said, some fans will see this as a bastardization of the series, some will just want new Guitar Hero, and some are just wanting a fix, and some will love it due to their love of Aerosmith, it's all up to preference.