The real kicker is the addition of a co-op multiplayer mode, however. Remember how ridiculous Potal 1 could get, once you got to later levels and you had all the elements together - moving platforms and walls, turrets, lava, crazy environmental design, and, of course, one guy with a portal gun?

Now add another person, and another set of portals, and some of the best writing and humor the industry has ever seen. That is the real draw of the game over Portal 1, the big step up.

As for the single-player campaign... well, Portal 1 had a tiny budget. Nobody knew whether it would succeed. Portal 2 had an astronomically higher budget, which translates directly into increased detail, more levels, more voice-acting and Jonathan Coulton songs, etc., etc. It's mostly just icing on the cake that is Portal 1, but... it's such a damn good cake.

I am not one to judge the value of a game base done length: I think that Portal 1 was better off for being the length it was, as Deathwatch Guard explained. And what it was was perfectly paced, and one of the best experiences I have ever had in a game. Easily worth twice what I paid for it.

I trust that Portal 2 is similar - minus the initial rush of discovery and new experience - so I fully intend to buy it when I have time to play it.

And yes, I convinced myself that it was worth the full price while writing this post.