I guess you haven't seen his Emmy-nominated performance in Something the Lord Made, his tight bit as a clever cop in The Woodsman or his fine Broadway turn with Jeffrey Wright in the Tony-nominated Topdog/Underdog.
He was actually a professional actor (as a teen) long before he was a successful rapper.
I love Mos and I think he's a great dude but I saw him in "Something the Lord Made," and although I loved the movie I thought his performance was good but not great.
I have not seen the Woodsman...
Saw Mos in Top Dog/ Underdog and he was a complete bomb. Mos put his head in his hands and sat on stage for almost 10 minutes without saying a word... finally he got up and walked off stage (all this in the middle of the play). Later we learned that Mos suffered from a headache and couldn't continue. I think Mos is better as a comedica actor than anything else...