I've gotten a little ways into White and I have to say, I've yet to see the drastically improved storyline people keep touting. Maybe it gets better, but so far it's just the same evil team with a slightly more plausible evil plan.
At least this time you're not the only person doing anything. For example, the Gym leaders finally play a role in the story and are not just kind of there for you to steamroll. The Professor also appears quite often compared to the previous four generations and actually does shit instead of going "Hey, you're doing great!" all the time.
Furthermore, the new evil team is much better than the previous ones, but also much more incompetent ("Try to take over the world, use only Patrat.") which is a shame since they are much more believable. Where the previous evil teams were just like "Here, this is the evil boss, he's evil and he's the boss.", Black and White actually are actually pretty interesting regarding the leader. And the motivation of the team or their leader/s seems to be clear from the beginning, but there's also some plot twists which I won't spoil here.
And, of course, there are the small things. For example, that Bianca's dad and the protagonist's mom actually were trainers before they became adults. That just adds at least a bit of character to an otherwise very bland stereotype. The motivations of your rivals is also much more polished with Cheren having a totally different personality than Bianca. I also like the fact that they try to fix up some plotholes and actually address questions like what happens if you battle inside of a house or whether Pokémon are partners or slaves to trainers.
So, all in all, it's still not
that great of a story, but it's definitely an improvement.