With each generation of Pokémon games, Nintendo usually makes an enhanced version of it, adding new features, story tweaks, and tweaking the roster of creatures. White/Black 2 are pretty much enhanced versions of Black/White, but the story takes place after the events of those games. I'm still reluctant to call this a sequel, because it doesn't do enough for me to shake things up, and the story is extremely bare bones.
I had felt that the Pokémon franchise had become stale and desperately needed a shake-up since the formula hasn't changed enough over the years. Black/White did change things a little, but it didn't do enough, and so I ended up giving it my lowest rating for the series.
This game has the same story template as every other game. Playing as a boy or a girl, you start out with one Pokémon and travel the world, catching more Pokémon, training them up, and battling your way to beat the Elite Four; the best trainers around. Your secondary aim is to collect them all; although that's almost impossible given you need to trade across the many generations of the games.
Your character is never really fleshed out, but I was less convinced by your character's motive. In previous games, you do get a sense that your character craves adventure, wants to be better than their rival, and wants to become one of the strongest trainers. In this game, it just seemed that your character was forced to take a Pokémon and went to get the gym badges because he didn't have much else to do.
As you play, you have more encounters with Team Plasma who have stolen Pokémon in the past, so your “rival” Hugh wants to take them down for stealing his sisters Purrloin. Team Plasma are trying to harness the power of Legendary Pokémon Kyurem to freeze the world. The story is weaker than the previous game, and poorly paced, so it feels insignificant until you are ready to take on the Elite Four.
There's a few new cities to visit, and since you start in a new town on the western side of the map, you will be visiting towns in a different order to the previous game. This can be interesting but then there's some annoying aspects like not having access to Daycare Centre until the post-game. There is quite a lot to do in the post-game, so it will keep you busy if you want to keep exploring and catching the new Pokémon that become available to you.
The game jumps on board the achievement hunting craze. There's a character who appears in the Pokémon Centre who gives you Hint Medals that act as an achievement list, and gives you medals once you achieve them. There's a lot of medals too, with various difficulties and effort.
The gameplay still suffers from the same problems. High encounter rates and easily-defeated Pokémon make the game feel more of a chore than something tactical and rewarding. There's a lot of defensive moves I never took advantage of because you can often defeat opponents in one hit. I would prefer fewer battles; but more lengthy, strategic ones. Many trainer battles put you up against a few Pokémon, rather than kitting them out with the full 6.
The early Pokémon games usually gave you the occasional tricky puzzle to overcome, but the puzzles in recent games have been very poor. This game doesn't change that; it's very bare-bones in this area, relying on pushing a few blocks or hitting a switch to progress.
Even though I am critical of the game, it is mainly due to having played so many of these games. If you are newer to the series, then you will probably be really impressed with it. I also think you would enjoy it more if you haven't played the first Black/White game, since the world will be completely new to you.