I'm sitting here listening to the soundtrack. This is really, really good. It feels like Halo. It pulls enough from past compositions, primarily O'Donnell's work, but also Rippy who did the Halo Wars soundtrack. It has a very cultural vibe to it, a lot of African instruments that give this a very "wild" untamed Halo feel. The music perfectly represents the Halo universe on an untamed world, while still retaining the signature fun and uniqueness of Halo's music.

I am really, really surprised not only by this soundtrack but by Spartan Assault as a whole. I really wasn't excited at all. I didn't even plan to get it. Then I heard a few comments that it was "fun". Hell, that's the truth of it. We need more games like this. Not necessarily in the mobile space, but in alternate genres other than First-Person Shooters. Halo Wars and Spartan Assault are both two very unique additions to the Halo universe, and I for one feel very happy to have them here.

While we're on this topic, I'd also like to point out that Spartan Assault actually does provide some interesting information from a fictional standpoint. For one, unless the splinter sect of Covenant featured in this game is something other than the Storm, this game indicates that Brutes and Drones are indeed part of the Storm faction. It tells us that Forerunners built constructs disguised as moons (queue Star Wars jokes) around certain planets (I imagine in case of Flood infection). And it tells us about certain vehicles and pieces of Forerunner tech and when they might have been inducted into the UNSC Spartan branch for use. While no specific timeline is given for the game, this does help us piece together a lot of the expanded universe stuff that happened after Halo 3 and leading up to Halo 4. It'll be interesting to see what is revealed when Mortal Dictata releases.

tl;dr: Buy Spartan Assault. It's cheap, fun, faithful (barring a couple misused sound effects) and much better than you're expecting (if a little short). And if you're a fan of classic Halo music, buy the soundtrack.