Looper is a sci-fi thriller about time travel, plus some other crazy stuff. In 2072, when the mob wants to get rid of someone, they send that person back in time to be killed by a looper, a hired assassin. JGL's character, Joe, is one of these guys. It's a bit hard to explain and I don't want to give too much away, but older Joe from the future (played by Bruce Willis) gets sent to the past to be killed by...himself, which is called closing the loop. Basically, Bruce Willis escapes before JGL can kill him and they chase after each other and try to find a way around this while a bunch of other things happen that you don't really expect.
I know that sounds kind of stupid, but I'm not usually a sci-fi fan and I would give this movie an 8.5-9 out of 10 probably. It's really sci-fi meets thriller meets Sin City. It's one of those movies where the more you think about it, the more you like it.
The weirdest part has to be JGL's face. I read somewhere that he sat in makeup for 3 hours each day before filming to be made up to look like a young Bruce Willis. He was probably the last person I'd expect to be cast to play that role, but holy crap it works. Within the first 10 minutes of the movie you can tell that JGL has all of his mannerisms down perfectly. It does take a little while to get used to his face, though.