Have you played Portal 2 yet? If not, you should probably get on that. I got the PC version on Steam and completed the single player portion on the first day, in almost 9 hours. People who played the first Portal know that it wasn't exactly the longest game in the world, but luckily Portal 2 mostly solves that.
The second Portal will take somewhere between 6 to 8-ish hours for most people, which is actually a good bit longer than the first one. I'm currently replaying the game with the developer commentary on. It's basically the same experience but with little nodes spread around the game you can activate to hear various developers talk about different features and design details of the game. It's really good and worth a second play through for.
Portal 2 also has some new tricks up it's sleeve, such as lasers that can be redirected with special cubes, light bridges that can be redirected with portals, pads that will launch you into the air and more. I especially liked the various types of fluid you can spread on the level, to make you go faster over it, bounce on it or even fluid that turns non-portal surfaces into ones that will accept portals.
I can't really say too much that you probably haven't heard already. The graphics are clean and a small step up from the first Portal, the environments more diverse, the voice acting is abslutely flawless and the writing is superb.
If you haven't played it, you owe it to yourself to give it a shot. And if you haven't played the first Portal... what???
I should also mention that the game has a separate co-op campaign that you and a friend can play together online. I can't say much about it as I haven't tried it yet. But I've heard very good things.
Portal 2 is available on PC, Xbox 360 and PS3 and is also available on Steam.
I'd give the game a solid 5 out of 5. Highly recommended.