Why didn't I have a recommendation for this one yet? Oh well, here it is, better late than never.

Portal 2, the amazing sequel to the amazing proof of concept that was Portal, is all that Portal was and maybe a little bit more. With a great story, great characters, great voice actors, great map design, and an upcoming map designer. What else could you ask from a Valve game?

With a SP lenght of approx. 6 hours, (If you don't rush it.) Portal 2 is worth much more than its current price tag. A must have for any videogame fan. If this game isn't in your library already, something is very wrong with you.