Well my Pokemon Black recently arrived and I opened the packaging like a starving psychopath that just found a chocolate bar. I'm not going to spoil too much for anyone so I'm just going to give you what I think of the game so far. Keep in mind that I've only just beaten the first gym leader(s?).
So far the game is amazing, however it doesn't feel like Diamond and Pearl were. If that makes sense. For starters the opening (as I'm sure most of you have seen already) seems very different from anything we've seen before in a Pokemon game, something about it makes the game feel darker. And the game does feel darker, I can't understand Japanese at all but from what I've seen it looks like the antagonists of this game are some kind of crazy Pokemon cult. Still I may be wrong because I'm not that far into the game and I don't know Japanese.
Another thing that makes this game different from the rest of the series is the new Pokemon that appear in the game. Most of what I've seen so far are some pretty bad or thoughtless designs and recycled ideas. (Do we really need another fire monkey, Nintendo?) I won't lie I have seen some cool-ish Pokemon on some of the websites but so far the only cool thing I've seen is the grass and water starters.
The battles however have barely changed at all. All that's different is that you can see your full Pokemon's body and that they are always moving. This makes battles feel more realistic and fluid. And believe me there is nothing cooler than seeing Tsutaaja (I think that's the grass starters name) tap his foot impatiently on the ground and fold his arms like a bad-ass. The music in the game is also top-notch as usual, the music also changes as the battle progresses. For example it will change when your Pokemon has low HP. It's little things like this that make the game really enjoyable. Now if you don't mind I'm going to go figure out where the hell to go next!
TL;DR
Not much has changed in this game apart from the new Pokemon and camera views.