I will not mention any spoilers, but lets just say that this episode actually affected me, on a physical level. Not many shows do this.
If you need to know only one thing, its that this episode deals with Sam and his father on the day he left Sam's life forever (when Sam was a child) . It ties together the previous 7 episodes. It helps to bring the viewer "full circle" in the world of Life on Mars.
Some may complain that the shows are getting repetitve, but I don't know what kind of TV they are used to watching. Compared to the rest of the shows out now, LOM is extremely creative and fresh.
Do yourself a favor and wath the whole season, and enjoy yourself. I know I did.