I personally am digging the music in ODST. It's bringing back the dark vibe that I think Halo 3 was lacking. Besides Halo i've only ever been a fan of horror/suspense games, it's nice when I can get a lil of that style in my favorite FPS:) Playing at night, the music, the mystery and being alone in New Mombosa, it's all good in my book.
Here's a good sample I found of some in game music, check it...
http://www.youtube.com/watch?v=RTr3bhgVbXY
[Edited on 07.11.2009 11:34 PM PDT]