Primary among things to consider before buying is the unchanged fret attachment: if you can't get comfortable with it you'll be in pain long before you even hit the '90s. Also, with the same in-game engine you'll still see bands that aren't really playing along, hear sound that isn't crystal clear, and deal with a touch-screen strumming mechanic that at its best takes a good bit of getting used to and at its worst isn't responsive enough for technical riffs. Ultimately Decades is a better game than the first On Tour, and both games can be genuinely entertaining. But, it's hard to see this as anything more than a 28-track expansion pack, and $35 ($50 if you get the bundle with the fret attachment) seems like a bit much for that.
Plays Like: Guitar Hero On Tour
Pros: Reasonably faithful experience; new campaign mode adds some life; solid multiplayer
Cons: Still uncomfortable for most; looks, plays, and feels exactly like last On Tour