Brick
One word review: Noir-tastic.
Multi-word review:
A film-noir detective story set in a high school. It may sound like an odd premise, but it works. To enjoy the movie you'll have to accept the seriousness with which the characters take their situations and accept the extremely stylized language. If neither of those present a problem, then you'll be in for a great time.
Essentially a murder mystery, Brendan's (3rd Rock From the Sun's Joseph Gordon-Levitt) ex-girlfriend (Lost's Emilie de Ravin) gets in with the wrong crowd and eventually ends up dead. Brendan goes on a mission to find her killer. It is tough to say much more than that without giving something away, so I won't.
The acting, writing and direction are all very good. Actors are given very complex and stylized lines to deliver. The writing is so stylized that it could easily become ridiculous, however the actors deliver the lines well enough that one accepts the language.
This film is definately worth seeing, especially if you are into noir or detective stories.
Full Film Geek Review (with spoilers)