In general, I really liked the soundtrack for Black and White. It's one of my most-listened-to albums in iTunes. I especially liked some of the more subtle things they did, like changing most of the route music slightly depending on the season (I tend to prefer the Spring themes), and the added percussion when you're walking along a route.
I particularly enjoy the music leading up to and succeeding the final confrontation with N. That is, Route 10, Victory Road (love the build-up through the gates, btw - it's almost as good as going up the stairs in the Tower of Spirits), Pokémon League, N's Castle Arises, N's Castle ~ Bridge, N's Castle, A Legend is Born ~ Reshiram, Prince N Battle, N's Farewell, and the Credits theme. This collection just seems to capture the mood around the journey. Also, for some reason I really like N himself. N's Farewell tends to make me almost cry.
The theme for Routes 2 and 3 is another of my favourites - especially the Spring version, as I mentioned earlier. I hear it a lot, I guess, as I end up biking back and forth along Route 3 to hatch eggs. And I'm not so keen on the Bike theme.
I don't like the Cold Storage/Twist Mountain theme as much as the rest; it just seems grating to me. Same reason why I never liked the Dragon's Den theme.
Then there's the Poké Transfer theme. The music that plays when it's loading on the DS you're transferring from. It's the only music from the game I don't actually have, which makes me sad. It's just so catchy!
I don't really like the battle themes as much in Black and White as in previous games. The only battle themes I really like are the Champion's theme, Prince N, and Subway Trainer battle. Speaking of Alder, his encounter theme is really nice. But the Legendary battle theme seems... well, I just don't like it so much. As for the Dragons' battle themes, they just seem a bit blaring. If only they'd managed something like the Dimensional Dragons' theme from D/P...
EDIT: Forgot the city music! >_< Castelia's theme is really nice. I also like White's version of Opelucid City, as well as White Forest. Weird... I prefer the music from the game I played second... Yeah, and Anville Town's theme is nice with the flute.
tl;dr:
I like most of the music a lot. Yay for Shota Kageyama et al!