Not as good as the original, but then so few sequels really are.

There's a secret in (retired and neuralized) Agent K's past, and Agent J goes to get him and de-neuralize him to restore his memory so he can tell people what the hell is going on. Two problems: Not even K remembers (he obliterated his own memory, but left himself clues to follow if he ever needed to), and MIB headquarters is taken over by some squirmy alien originally posing as a sleek sexy babe. (You'd think they would be able to scan even sleek sexy babe-aliens to avoid alien takeover of HQ, but never mind that.)

Along the way is some humor (not as much as the first one), some action (still not as impressive as the first-movie action).

It's an OK movie, but it won't make your "great sequels of all time" collection. Wait until it gets into the second-run theaters or rent the video when it comes out. Worth seeing, but not worth a top-of-the-line ticket.