Just downloaded the soundtrack off iTunes.
My initial impressions (which may change once I see it paired with the film) are that it's serviceable music, but nothing to get excited about. Giacchino is a good composer, in that his scores always seem to support the films and work emotionally with whatever scene he's scoring. But I've never walked out of a theatre thinking the music was something that stood out; for that matter, I can barely remember how any of it goes, even for films I've seen numerous times ("Ratatouille").
The main theme (Heard in track on, "Star Trek") sets the right atmosphere, but does little beyond that. It is short, bland, and unmemorable, simply rising three notes, descending one, leaping down a third, and returning to tonic. It lacks any sense of direction, drama, momentum, or interest. On the plus side, the orchestration chosen does remind me of a lot of the great "Trek" themes of the past. It's really more of a leitmotif than a theme (a theme for a typical Trek film would feature several long, sustained musical phrases, perhaps a B section, and a return to the opening idea). The problem with leitmotifs is that there has to be something really special about them to make them stand up as a musical idea, since they present so little information. For example, John Williams wrote over 500 possible motifs for "Close Encounters of the Third Kind" before settling on the "right" one.
Tentatively, having not seen the film, I give the soundtrack a C. Average, but nothing special.