The trailer for Edmund McMillen's The Binding of Isaac is about half gameplay footage, showing a top-down, single-screen shooter reminiscent of The Legend of Zelda. The other half is a montage of creepy puppets, screaming, and a naked man. The trailer was directed by James Id, also responsible for the legendary Super Meat Boy trailer.
The trailer confirms the September release window for the Mac/PC game (a Linux version is coming "eventually"); previously, McMillen called September a "safe" estimate, and aimed for late August. Also confirming that new release window: it's pretty much the end of August right now.