2nd best game I've ever played, 1st being the original Pokemon Black and White. As someone that's a huge fan of the RPG genre, this game has done it best, taking revolutionary games for the genre such as Skyrim, the Zelda series and Undertale into account.
Pokemon Black and White 2 holds a very compelling storyline, amazing music and atmosphere, as well as having characters that make the journey seem more exciting and worthwhile.
I've played through the game roughly 40-50 times (100% completed, including Pokedex), and countless other times just beating the Champion.
The Gen V games explore darker themes that the rest of the franchise fails to do; that humans could actually be corrupted and have ulterior motives. Other games look at the entirety of the Pokemon world as just one big utopia, a utopia in which nothing perilous to the population could happen. Of course, there are the antagonists, which are the groups of people trying to steal Pokemon. But Pokemon Black and White (as well as Pokemon Black and White 2) actually goes quite into depth about why these antagonists want to do this, and this forms a strong foundation for the main story. The rival in this game, Hugh, also has a backstory that some find somewhat annoying, even though it's about something very meaningful to him that was stolen.
I may be the slightest biased, because this game also presents to me memories and I reminisce about the phase of my life that I bought these games. But this game, is really just phenomenal. You won't be disappointed.