Upon seeing the film, two pieces of music on the soundtrack caught my attention - "Deportation" by score composer Gustavo Santaolalla, and the memorably melancholic "Bibo no Aozora" by Ryuichi Sakamoto, and these two haunting tracks were enough to convince me to buy the cd.
The two disc compilation, like the film, is a mixed bag, switching back and forth between Santaolalla's oud tracks for the Moroccan section, raucous Mexican party music for the wedding scenes, and Japanese pop and hip-hop for the Tokyo section. Personally I'd have been happy with just the Santaolalla and Sakamoto - the Mexican stuff is mostly simplistic and uninspired, with only "El Besito Cachicurris" displaying any complexity of melody or arrangement; and the dance music from the Japanese scenes feels out of place here, with Earth Wind and Fire's "September" in particular sticking out like a sore thumb (a great song, just not in this context).
But Santaolalla's original score is hypnotic and atmospheric, and justifies the purchase.
By the way, don't be put off by the "music from and inspired by" label - this is no cynical cash-in: the extra tracks mesh well with the ones featured in the film, and as the director explains in the liner notes, often inspired scenes in the film, rather than being inspired by them.