The man was fantastic in First Class, and was one of the main reasons to watch that film. He was also great in Prometheus.
I've felt that Ubisoft made these games specifically with film rights in mind. They feel extremely cinematic and there is a decent story here that would translate well to film. I'm curious to see where/how this production goes.
Fassbender is great in basically everything he is in. After Prometheus, I think I will watch any movie with him in it just for his performance, and there are VERY few actors I'll say that about. Saying he'd be great in Assassin's Creed is obvious; he'd be great in anything.