Sean Penn is one of the best actors alive, in my opinion - he is not afraid to portray unnactractive, unnapealing characters making them jump out of the movie screen totally attractive and most appealing: you can't take your eyes off of him.
RollingStone.com: "The sheer brilliance of Penn's performance anchors the film. Jimmy may have gone straight, but there's a coiled intensity in him ready to spring. Katie's death is the catalyst. There is something in Jimmy that even his wife, Annabeth (Laura Linney), and their kids can't touch. In a stellar career (Dead Man Walking, Sweet and Lowdown, the upcoming 21 Grams), this may be Penn's most potent two hours onscreen. Do you want to see screen acting at its riskiest and most riveting? Watch Penn."