All right, here are my opinions (and I emphasize the word "opinions") on the new music:
Wild Pokemon Theme- is now 20% cooler. The change in pitch is welcome, and the tempo seems to have been altered making it sound slightly more epic.
Rare Wild Pokemon Theme- Why didn't they change this to match the new Wild Pokemon Theme? It sounds out of place now.
Trainer Battle- Sounds mainly the same, I never liked this one that much anyway.
Rival Battle- This one sounds okay, it might grow on me as I hear it more.
Gym Leader Theme- I'm not sure they should've changed the instrumentation on this one. It sounded almost perfect in BW1, now I don't know what to make of it.
Gym Leader's Final Pokemon Theme- I swear there's a mistake in this. About 2 seconds in, it sounds like the tempo gets too fast and then it skips back down to the usual tempo. It doesn't sound right. Other than that, it's good.
Team Plasma Theme- I don't really like the intro, but otherwise pretty good.
Akuroma's Team Plasma Theme- Like with the Rival theme, I don't really think much of this one, but I'm gonna give it time.
B/W Kyurem Theme- Same as Rival and Akuroma themes (and a lot of the new ones actually).
Iris' Theme- Better than Alder's, but still not a proper Champion theme. A bit too "twinkly" IMO.
World Tournament Final Battle (the one that plays when you fight Akuroma)- This one's already growing on me.
Kanto Leader Theme- I like this one, it has a retro feel to it, as it should.
Sinnoh Leader Theme- This is another theme that I feel they did right, it sounds like the original, but with extra background music and stuff that enhances the tune.
All the rest of the World Tournament themes- Very meh. A lot of them have unfitting instrumentation and don't sound very good.
what? Rustboro City music???
http://www.youtube.com/watch?v=uoYtPJSlizA&feature=plcp
Rustboro City isn't in Unova...
That's not even Rustboro's theme.