Geometry Wars pretty much defined XBLA as a viable platform. So where are all the sequels? From Ben Ward of Bizzare:
We're playing our Geometry Wars cards close to our chest right now. As you know, we've just announced Geometry Wars Galaxies for the Nintendo platforms, GW: Mobile for mobile phones, and we've recently released the game onto Steam too....So there's a lot going on but that doesn't mean we've forgotten about the Xbox 360...
And then he should have added:
...it just means we are making WAY more money doing other stuff. WAY, WAY more.
I really enjoyed Geometry Wars Galaxies when I played it at E3. The Meteos-style, planet level approach proves there's a lot more meat to the franchise than an XBLA title can exploit. But it's good to know 360 owners will see a new title eventually.