ODST has some of the best atmospheric and ambient music of any game i've played.
Worth noting that due to how music works in Halo games the music can be confusing. They use a dynamic system to splice together and transition from/into small, 2-3 minute tracks of music that are designed to be interuptable and resumable.
So for each of these links, it's actually 3-4 seperate tracks, each being one of those mini splicable tracks. Some of them are purely ambient/idle tracks, others are "battle" themes to play when combat is triggered, others are event/actual theme music (for each link, an actual theme is the start of each video/music track befoore going into ambinet/battle themes and maybe one other main theme), etc. But ODST in general is a very moody game so even the event/theme music and battle themes should qualify, the actual ambient ones doubly so
https://www.youtube.com/watch?&v=BwS056zXmLk
https://www.youtube.com/watch?v=AQRH6kLMa1k
https://www.youtube.com/watch?v=utg1wmeToNc
https://www.youtube.com/watch?v=bmWbQTtt2dY
https://www.youtube.com/watch?v=PitfyNbb6GE
https://www.youtube.com/watch?v=TgQspLykHUM
https://www.youtube.com/watch?v=FpgKoJJKRXI
Also, even if you hate Halo and think it's casualized console trash; give them a listen. ODST's soundtrack is fucking phenomenal, and it's way more experimental a game then any of the other halo titles by a huge margin, being more Noire with some light Cyberpunk elements then space marine stuff.