Gameplay and story improvements are great, but marred by other huge steps backward. Not as good as HeartGold/SoulSilver.
The new Pokemon are diverse and plentiful. After fighting the same old Pokemon everywhere, Black and White starts with a clean slate; you won't see any Pokemon from previous generations until you've beaten the Elite 4. This generation introduces the most new Pokemon of any of the previous generations (... though discounting normally unobtainable event Pokemon, Gen 1 next in line would have more).
Black and White also offers new battle modes, many new skills and abilities, a much improved online mode, and a separate online outing that is currently unavailable but sounds interesting.
So why am I docking Black and White as worse than Gen 4's HeartGold/SoulSilver? User Interface.
Black and White take 4 steps forward, and 5 steps back. The use of the touch-pad is extremely poor. Unlike HeartGold/SoulSilver, you can no longer use the touchscreen to access the in-game menu without first clicking a right hand button, advance conversations, lock on the running shoes, use your registered item, skip the intro movies, navigate the main menu...
Instead, the touch-pad is used for the online, wi-fi, and infrared components, collectively known as the C-gear. Unfortunately, this is utterly useless 99% of the time while you're playing alone. There could have been a toggle in the options menu, or the C-gear and in-game menu could have swapped with the C-gear mapped to the X button... but I can't stand the way the controls are now set-up. Navigating the interface requires a lot more button pushes, which means a lot more adjusting my hand positions and a lot less comfort. As a guy who works on a computer all day, the last thing I need is more stress on my hands.
The item interface is worse, the pokemon storage system is worse, the battle interface with its awkwardly shaped buttons is worse (though I do appreciate the presence of a clock on-screen)... I would have expected such a poor user interface from Diamond and Pearl, the first Pokemon games on the DS, but not from Black and White, likely the final Pokemon games on the DS.
I am also not a fan of the new 3d graphics. I'm playing this on a DSi XL and the pixelation is killing me. Walking into a Pokemon center to heal is a headache watching details pop in and out. The ground textures look very good, but world objects are distractingly pixelated and ugly. In battle, your own Pokemon look awful since they're so close to the screen. I'm baffled as to why they didn't make the back sprites at a higher resolution, considering that your own Pokemon are essentially the entire focus of the game, yet the most common view of them makes them look so ugly. There is also no more option to have the first Pokemon in your party follow behind you on the world screen, probably due to the difficulty in rendering 649 possible different Pokemon in the new 3d environment.
I appreciate Black and White as the next major step in the Pokemon franchise, but I cannot forgive its flaws and failures next to previous franchise offerings. I look forward to continuing my adventures in Unova, but GameFreak could have done better.