If you think season 3 finale was awesome, well, this goes way beyond that.
Starbuck returns, claiming she's been to Earth, not knowing that everyone saw her blowing up in space, and she keeps saying they're going the wrong way. Baltar finds himself in the middle of a cult to his figure, which only gets him in trouble. Meanwhile, the four "new" cylons try to keep their lives going on as they were before.
Besides all that, the space battle scenes are among the best I've ever seen on tv.
In a nutshell: this episode is SUPERB.