I actually thought Michael's acting in "Bad" was good.
The film itself is interesting because of the concept behind it. Michael goes to the subway with his buddy's to try and prove himself to them but then he realizes that what they're doing is wrong, so he refuses. Now the part that's interesting is, when Michael yells "You ain't bad, etc..." and then it turns from black and white to color, the whole sequence with the song is Michael (or the character Daryle's) imagination, starting after he yells at Wesely and the rest. He imagines having his own troop, his own back up and bringing it to Wesely and his troop. Then, at the end of the dance sequence, he and Wesely come to a truce, but when it fades back to reality, all it really is, is Weslely and the rest leave Michael alone in the subway, they sort of abadon him. So the whole dance sequence is meant as a dream, and the reality is just Michael falling out with his friends.
On top of that, the "Bad" video has some of the best dancing I've ever seen, its well acted, a really interesting story line and set up. Its one of Michael's absolute best and underrated because morons thought it was Michael trying to be "hard", when what he was really doing was sending a message that you didn't have to be violent or criminal to be cool.