Since the actor Sam Rockwell is so different in all his movie rolls it's difficult for me to say something coherent about them except that even when I don't enjoy the writing (as in "A Single Shot") I can't take my eyes off of what he's doing on screen.
When I was sitting down to select a couple movies to suggest I totally forgot Rockwell was in "The Green Mile" because the character he plays (a crazy prisoner who taunts everyone around him in the most foul way) seems to be someone whole and other, not a creation coming out of a writer and and actor.
I compare that role to his comic character in "Galaxy Quest" (as an "uncredited" crew member who knows he won't survive "the episode") and his cocky con-man in David Mamet's "Heist." Again, they don't even seem to come out of the same person.
This makes it incredibly fun to watch Rockwell.
Recently I've seen two movies in which he's shown a "softer" side. His characters keep their wackiness and an engaging sense of self-directed humor, but also show vulnerability.
In The Way Way Back Rockwell plays Owen, the manager of the Water Wizz water park. He befriends a kid who is having a tough time with his mother's overbearing boyfriend (Steve Carell) and his new family situation.
In Laggies Rockwell plays the divorced father (Craig) who manages to play it cool and mature when his precocious daughter (Annika—Chloë Grace Moretz) brings home a 28-year-old (Megan—Keira Knightley) who is escaping from her life. It all makes sense when you see it. In this movie Rockwell has one of the most romantic scenes in any movie—when he visits jail to get Megan out after an accident, and tells her how he feels. Big emotion, held in check. It takes your breath away.
So I recommend you get some popcorn and watch those two movies in that order. And then if you haven't already started keeping track of Rockwell's movies, start catching up so you don't miss out.