I checked out Portal Reloaded this evening. It adds a whole new dimension to the game, or rather two. Aside from the traditional orange and blue portals you can also utilize a third green portal that allows you to travel between the present and the future. You can move a cube in the present, walk through the time portal, and find that the cube is where you left it. It’s really quite trippy, imagine your past actions having an impact in the future, and immediately accessible through a time portal!
If you like Portal or Portal 2 I’d give this a try. I’m only on test chamber 4 so far, and I can already tell my brain cells are going to be in for a ride! 😛