I just pick up Gemoetry Wars 2 because of friend recommendation. Is on sale right now for 400 points (50% off) and the discount is available to everyone. I also recommend Strania and Side-Vower add-on, Ikaruga is you don't have the GC/DC version, DeathSmiles II (not on XBLA, but full game is downloadable), and Triggerheart Exelica. Also the upcoming Guilty Gear revision, but that is not for all the people.
Waiting for Smash U? In the meantime, duke it out in Anarchy Reigns!