Sanaa Lathan as (Leah) did a great job playing the girl that just found out that guy she was digging is a psycho.
Michael Ealy as (Carter) was okay in his role as the psycho and obsessed boyfriend but I felt that they didn't give Michael enough to work with to really bring his character to life. He had no back story and no build up to his psychotic break which made his character more annoying than scary and gripping.
Morris Chestnut as (Dave), Leah's love interest and current situation before Dave comes into the picture. Morris did great in the little part he had to play in the film. There was one scene that he delivered that really helped shrink Dave down to size and I loved the whole dark chocolate VS caramel going on in that scene; it was great! If you've seen the movie you might know what I'm speaking of. If not I will not spoil it for you.
There were others in the film that did a great job as far as the roles they played like Holt McCallany as (Detective Hansen). Over all the actors were believable with what they had to work with.