While there are some issues with Guitar Hero 3 it is still a fantastic rhythm game well worth having.
Good:
Best song list in a guitar hero game yet. Mostly master tracks. More diverse songs and breadth in genres. Online play is great fun. Les Paul guitar is also the best yet. Challenging songs for more experienced players. Cool new look to characters, menus and stages. More bonus stuff to unlock. Hammer ons made easier for new players. Co op career. Cutscenes that don't retract you from the experience. Slash and Tom Morello. Motion capture is generally good. Fun at parties, especially if some of you are guitar hero veterans.
Mediocre:
Boss battles aren't that fun. Strange note charts make some songs a lot harder than they should really be. Extremely difficult songs towards the end of the game. Some songs just aren't fun to play. The drummer plays like a robot. The career starts to feel old quite soon into the game.
Bad:
Ton of in game ads and sponsored unlockables, really awful if you consider how much money Activision makes already.
Basically if you liked any of the Previous Guitar Hero games or liked Rock Band GH3 is definately worth picking up. Whilst the takeover to Neversoft developing the game may have detracted from the Rock God theme the game is still very fun. Some songs are made a lot harder than they really should be through bad note charting but if you like a challenge there is definately one here.