So I picked up Outland on XBLA this week, and I can tell you it was a well-spent $10.
If you haven't heard of it, Outland is a 2D platformer with a great color polarity system akin to Ikaruga or Schizoid. There are light and dark forces in the world (blue and red), and you need to switch between your blue and red powers to defeat enemies and solve puzzles.
On top of a great platforming adventure, Outland offers an incredibly enjoyable artistic style. Like Braid, or Limbo, Outland's charm comes in large part from its unique appearance. Using very fluidly animated 3D models on a 2D plane, combined with the entirely black foreground accentuated by bright glowing colors, Outland is just as much fun to watch as it is to play.
I bought the game for the co-op, in which you can play through the entire story mode, as well as co-op specific challenges. When I tried it online with a friend, we suffered lag bad enough to make the game unplayable... we tried it with each of us hosting, with no change. I don't know yet whether it was a fluke with our connections, or indicative of a problem within the game itself.
I don't want to warn you off of the multiplayer side of the game based solely on my one attempt at connecting online, but if anyone else out there was experiencing problems with the online co-op, feel free to let me know.
Connectivity issues aside, as much as I was interested in playing the game cooperatively, it occurs to me that this may be one game better enjoyed as a solo adventure. The co-op seems less like working together, and more like both going through the same content at the same time.
Not to say it wouldn't be fun to play with a friend, but I don't think it was designed around the co-op experience in the way I was expecting, which is to say like Schizoid does.
Either way, it's a pretty fantastic game, and I'd highly recommend at least checking out the demo.