The story takes place a few years after BW2. By now, Unova has changed a whole lot; the game feels like you're reconnecting with friends you haven't talked to in a long time, so you'll be able to see how most of Gen V's characters have grown.
Hugh has become an advocate for Pokemon, and helps take care of abandoned Pokemon, ala Mr. Fuji. He can be battled once in the main game, and daily in the post-game. In the main game, beating him will convince him to give you a rare Pokemon, because he thinks you'd be the best person to bring out its potential and make it happy.
N is the Champion, having learned a lesson about whatever. Iris took over the Opelucid Gym after Drayden retired or died. The Elite Four are Benga, Shauntal, Caitlin, and a new character. Marshall followed Alder's footsteps and rams the region, and can be battled in the post-game or the PWT.
Team-wise, the villains are the Shadow Triad or a new character that just rips off N's schtick. They want to get revenge on N and Unova by taking over the region city by city, Conquest-style. Your character will have to liberate these cities when you get to them. These guys are themed after chess or some shit, and their outfit's color is either black or white, depending on your game.
The Gym Leaders are the Striaton trio, Burgh, Roxie, Cheren (Roxie and Cheren can be faced in either order), Elesa, Skyla, Iris and Marlon.
The region is largely the same as it was in BW2, but enhanced, and you start at Nuvema Town. Musicals and PokeStar Studios are back; PokeStar lets you do "remakes" of classic movies, and it has its own set of new films. Musicals are now a proper rhythm minigame, and you can get Ribbons from them, in addition to props. A Pokemon's size and speed are taken into account, so you should choose songs that suit their style.
PWT, Black Tower/White Treehollow, Battle Subway are back. The latter has been expanded to have routes all over the region, making for easy transport.
