Will Smith was hilarious as Agent J, who travels back to 1960s to stop a nasty alien from killing his partner Agent K, played by Tommy Lee Jones. Josh Brolin played the young Agent K, and he was right on the money impersonating facial expressions and a voice of Tommy Lee Jones.
Not to give up too much: there is a lunar prison base, cool blasters, new alien forms, one-wheeler motorcycles, time travel, and, oh yes, the jokes!
The right amount of special effects and a very crafty story line, made MIB3 a fantastic choice for a whole family enjoyment. The movie is rated PG-13 but younger kids should be just fine. If you haven't seen it yet - I strongly recommend it.
Video: MIB3 official website