I grabbed Geometry Wars: Retro Evolved 2 yesterday.  It replaces Geometry Wars as the best $10 you'll spend on XBLA.

There are enough tweaks to the game to make it feel fresh, as well as vastly superior to the first GW.  The biggest change is in how your score multiplier works.  Rather than just killing enemies to gain a multiplier, you now have to collect geoms - small green shards - from your defeated foes; the multiplier goes up by one with each that you collect.  When you die, the multiplier does not reset.  This flips the game on its head, as you'll need to be a bit more aggressive in collecting geoms in order to get a high score.

You should read Jeff's review for all of the game modes and secrets and stuff.  I will say that the biggest surprise for me was that my girlfriend and I had the most fun with King mode.  Since she's not an avid gamer, she has some trouble with moving and shooting at the same time.  In King, you'll either be doing one or the other, not both, making it much easier for her to play competitively.  When we switched to co-op mode, we went back and forth between one person controlling the guns and the other controlling the ship.  It seems to be more fun for the driver, but the constantly - and unpredictably - changing path is a nice challenge for the gunner.

I only have one knock against the game, though it's not something I particularly care about.  There is no online multiplayer, which does seem a bit odd.

***** - 5 stars!