I never got into the first Geometry Wars (I'm just bad at shooters in general) but I got the new one, Geometry Wars Evolved 2, and it's fucking incredible. There's 6 different game modes that are all pretty ingenious and interesting, and it's just SO addictive. You guys need to get it and then sign into your xbox accounts every once in awhile so I can compare scores. It's great.
Actually these next 5 or 6 weeks are supposed to be insane for awesome Arcade titles. Braid next week (puzzle/platformer thats getting TONS of hype for being totally good) Galaga Legions which is made by the PacMan CE guys, supposed to be better maybe than even Geometry Wars 2, Bionic Commando remake and some others I forget.