Direct links to the regular soundtrack samples:
http://soundcloud.com/neil-davidge/awakening-ost-sample/s-UYHgm
http://soundcloud.com/neil-davidge/to-galaxy-ost-sample/s-CQAvt
http://soundcloud.com/neil-davidge/ascendancy-ost-edit/s-avqMe
http://soundcloud.com/neil-davidge/revival-ost-sample/s-zxyMw
Halo 4 sound track samples and details here.
More articles: http://www.huffingtonpost.ca/2012/08/22/halo-4-soundtrack-neil-davidge_n_1819736.html
http://www1.rollingstone.com/hearitnow/player/neildavidge.html
(thanks Hypertrooper)
Limited edition, with remix album:
Besides the standard edition release, the 23rd will also see the release of the 2-disc Special Edition box set which includes the soundtrack as well as 14 remixes from electronic producers and rock musicians. While the standard edition will run you about $13.98 USD, the Special Edition will set you back $75 and include a 70-minute DVD with behind-the-scenes footage featuring the creation of the soundtrack, a hardcover book focused on the making of the soundtrack, a print signed by Davidge, a 12" disc featuring Cortana and the Master Chief, and an exclusive Avatar tee download code. You can order that directly from Halo Waypoint.
Here's the full list of remixes, which include DJ Skee, Caspa, Sander Van Doorn & Julian Jordan, Gui Boratto, KOAN Sound, Matt Lange, Andrew Bayer, Norin & Rad, Alvin Risk, Bobby Tank, Maor Levi and Hundred Waters, along with Apocalyptica and ex-Smashing Pumpkins guitarist James Iha.
Very different direction than the rest of the series, which was probably the right thing to do, rather than try and iterate on Marty's work.