So... CoD4, Assassins Creed, or Guitar Hero 3?

I just cant make my choice.

I've been dying to get Assassins creed for a long time, but a friend tells me It does get boring, and the bad reviews dont help either.

Besides, I recently became a FPS fan, and I loved CoD2,and I love GH2, so it doesn't help either

Its'just that I dont want to waste my money, and I really want Assassins creed, but I dont want to regret buying it :(