Portal

The game makers over at Bethsesda are apparently Portal addicts (and so is just about everyone that's played it... great game).

Now they are such addicts that they had to go an make a new map for portal, and let me tell you, it's a damn doosey. It's fun, it's interesting, and it has some impressive new gameplay functions that Valve didn't throw at us in the official game.

It also looks nearly as good as a "real" level and even re-uses some of the GlaDOS voice snippets as you go along. All of it makes for a good time out.