Echoes+ is currently in Creators Club playtest and will hopefully be released on Xbox LIVE Indie Games in a week or two.
Anyway it's the sequel to the Binary Zoo freeware game Echoes (no way!) which someone on here might have heard of. Doubtful but you never know
6 different game modes, 4 difficulty settings, 100 Trials (Achievements), multiple powerups and weapons...and other stuff.
Feel free to make derogatory Geometry Wars comparisons...you wont be alone
Youtube playlist showing a few of the game modes.
Thanks for your time.

, also I'm guessing xbox indie has about a bazillion arena games by now. Gimme that tasty vertizontal action any day