Cinema Blend included Groov on their list of 5 Actually Good XNA Games For $2.50 Apiece! Along with NextWar: The Quest for Earth, Johnny Platform's Biscuit Romp, Philip Muwanga's Hexy Trench, and Miner Dig Deep, Groov was deemed a game "you should know about, unless you hate fun." Here's their whole write-up on Groov, awesome part emphasized by myself.
What at first appears to be a more-affordable version of Geometry Wars quickly distinguishes itself as some sort of music/rhythm/shooter type-thing-game. If that description made no sense, I'll clarify; every enemy in the game moves to a certain beat, and your bullets fire at that same beat. Once you hit an enemy and "kill" it, it will turn into a harmless, white version of itself. That white enemy will then die out at a time that is appropriate for the beat of the song. Each different type of enemy makes a different musical sound when it dies, and your bullets make piano...
You know what? Just download the trial. It's like Geometry Wars mixed with Beethoven and Jesus. That's all you need to know.
Niiiice.