Michael has never "acted" as anything other than himself, regardless what the names of his characters have been. Sorry, but MJ was merely pretty good for someone who isn't a real actor in his roles. And moreover, roles that he could believably play are extremely slim. If you think the audience would accept Michael Jackson as somebody's pal at the office, you are borderline psycho.
No offense, of course.
He can play Michael Jackson perfectly, since he's Michael Jackson, which is why the parts he's done in the past have been entertaining. There is nothing I have ever seen to suggest that he's got the chops to make it a career where he plays
a bunch of different people and personalities effectively. Of course, there are a lot of actors who sound the same in all their parts, but they have the advantage of being much more average than Michael Jackson.
He's already unbelievably gifted at so many things, so there's really no reason for me to pretend he's a good actor too; certainly not in the same way you'd call a professional "good." But for a non-actor, MJ is real good.
And anyway, I thought this movie which almost certainly isn't going to happen (not in 2009, anyway) would be ABOUT MJ rather than featuring Michael on the cast.
I mentioned this before, but a Michael Jackson movie with the right writer would be great. I can't think of a better way to inform ignoramuses about what really happened with those allegations without asking them to research. And of course, a film about his life would be entertaining as hell. Probably wouldn't be as good as The Jacksons flick, though.