This week just the one XBLA release called Chime. Single player game seeks significant gamer for musical puzzle fun. Me: unique, compelling, creative and demanding. You: quick-witted and open-minded with sharp reactions and a deep love of music. Let’s get together and play something beautiful. Featuring music by Moby, Paul Hartnoll (Orbital), Philip Glass, Fred Deakin (Lemon Jelly) and Markus Schulz.
Chime only costs 400 
and 60% of that will be donated to charity so you do a good deed and get a game for spending a couple of $/£. More information can be found on the Marketplace, there is also a trailer below as screenshots do not really do the game justice.
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Lovely little game, that. It’s what Lumines should have been.
Great game – a definite purchase at only 400 points, and with 60% going to charity.
Like Trez said, it’s very similar (only better?) to Lumines on PSP