Put in a couple hours last night and loving the game so far. Adventure mode is actually pretty cool. If you can get over the idea of 3D play spaces in your geometry wars, it's tons of fun.
Only downside for me so far is some of the "feel" in pacifism. Pacifism was my favorite mode in Geo2, as I'm sure it was for many people, and I played the hell out of it. I find that going through gates and killing blues here isn't quite as satasfying for two reasons. One, the gates don't "pop" quite as satasfyingly when you go through them and two, it feels like the geoms pop up slightly late when you kill the blues. It's like the score shows, then the geoms pop up. These two things combined make the mode slightly less satasfying.
Overall though, this is a very worth sequel to my second favorite XBLA game (the first, obviously, being trials evolution).