I saw this at Sundance in January. Here is what I said at the time:
This is the best movie I saw at Sundance this year. Duncan (Liam James) is a shy, quiet teenager with no self esteem. As the movie begins, he and his mom (Toni Collette) are driving with her boyfriend Trent (Steve Carrell) and his daughter. They are on their way to Trent's summer house by a lake in a small lakeside town (think Martha's Vineyard).
Trent is encouraging Duncan to be more outgoing, but in the most insulting ways possible. And Trent's daughter acts like Duncan is a 5 year old kid she is forced to babysit. His mom has no idea that Duncan is being treated so bad, or she is turning a blind eye so she can make her relationship with Trent work.
Duncan eventually meets Owen (Sam Rockwell), a fun guy who manages a water park. Owen befriends Duncan and starts watching out for him. He's like the perfect big brother. He gives Duncan a job at the water park, and Duncan starts to come out of his shell.
This is a really nice movie. I felt a lot of empathy for Duncan, and it was a real joy to watch his transformation over the course of the movie. Sam Rockwell is entertaining as always, and this is some of his best work. Owen is the type of character who is always 'on', always quick with a joke and entertaining everyone in the room.
Allison Janney is a lot of fun as the divorced, sassy neighbor who always seems to have a drink in her hand. And Steve Carrell gives a performance that is a lot different from his comedy roles. He really isn't a nice guy here, and he is very convincing in the role.
AnnaSophia Robb plays Susanna, the cute girl next door who develops a crush on Duncan, and this story line is the one that the movie short changes. There is a little bit of a nice, innocent young romance between the two, and I would have liked the movie to show a bit more of that. Early in the movie, Duncan has so little confidence that when Susanna practically asks to hang out with him, he can't even say yes. By the time Duncan has come out of his shell and is showing some interest, the movie is almost over.
I really enjoyed this movie and the performances. This is one of those movies that could have gone on for another hour and I wouldn't have minded. Highly recommended.