Found this on twitter yesterday and I'm surprised it's not on here yet. The game Hexic HD is free on XBLA. I don't know for how long.
Here's a link:
http://marketplace.xbox.com/en-CA/Product/Hexic-HD/66acd000-77fe-1000-9115-d802584107d1?cid=search
An old game, but reviews are good.