It's available for download at TrekCore. I need more because I've been listening to the same minute and a half of music for two hours!
I'm a Giacchino fan and this is all him. If I had to compare it to anything else, I'd say it has a Hunt for Red October by way of Lost sound to it. I'm sure someone can tell me what classical composers that kind of sound is lifted from. Horner has used it, Poledouris used it, Jarre has used it. It's a "big lonely nautical" sound. And it's got some Zimmer / Arnold style percussion. So it's what I expected from Giacchino: A classic sounding score with modern touches.
As far as what I think it "is"? It sounds (to me) like Jim Kirk. It sounds like the punk kid taking his destiny. ("No escaping, that's for me!") If I had to guess a plot point I'd say it's joining Starfleet or taking command or some such pivitol moment. Just a guess.
I'll be curious to see if this movie has a big "Main Title" or if it will just have a title card and go right into the movie. We might not get the big "THEME" until the end credits.
Giacchino took a lot of Mission: Impossible music from the series that wasn't just the theme for his M:I3 score, kind of like how Horner used lots of TOS music throughout TWOK (Khan's Pets / Kill Admiral Kirk) that wasn't just the Courage theme. Won't surprise me a bit if Giacchino takes the same approach. I also think that the overall score will be more TWOK than TOS, just because I think I've heard that's Giacchino's favorite.
But we'll know soon, won't we?