I've totally played that game!! My friend had it. It is specifically made for Gackt, I don't know why they named the main character something else since he is the main character. There are even interviews with him as one of the egames special features ;) It was FUN!!

And about the Gackt look-alikes - some of those are pretty good, but towards the end I almost start to think it is Gackt dressing up like the characters rather than vice-versa...