You wanted to know what was different about this Pokemon game. I'm not far in yet, but there are some significant things I've noticed. The game has some of the best polish on its small details I've seen in a long time.
The general formula (Catch pokemon, train pokemon, beat other trainers) IS the same. But the small details are really, really nice.
For instance, in all the games your early options for Pokemon include a normal/flying Bird, some kind of mammal-based normal pokemon, and a worm-ish pokemon. XY does, too, and then they also tossed into that same route another option for each of those types from earlier generations. So right off the bat, you get to start making actual decisions about your party. And if this trend continues, it'll mean you don't always feel like you need to use <insert pokemon> because it offers new type coverage. Even then, you'll get to choose.
And then in the first forest, they add Caterpie (and the second stage caccoon pokemon), plus Pansage and Panpour (and possibly Pansear - haven't found it yet), which are elemental monkey pokemon. So now I have a grass type, and if I started with Fennekin I'd have all three starter types. Plus, you can get a Pikachu here (though it's a spawn rate akin to the original red/blue, but the pokedex says it's the only place to get one, so damn it all I'm going to).
Every other game spoon feeds you the pokemon, because they really want to focus on their new set. This game seems to be saying "Screw that, let's give this is a pokemon game, give them a crap ton of pokemon).
And it's awesome.
They also gave happiness a bigger effect in this game. Now, it can actually influence your pokemon's performance in battle, with a happy pokemon more likely to shrug off status ailments, hit the mob, etc. So there's reason to care about and invest in your team even along the way. And you get to raise happiness using the Poke-Amie minigame. At its basic level, it's sort of like a reduced Nintendogs. Then there's minigames you can play with them that also buff their happiness stats.
And the world is more alive and playful than ever before. I turned on a television, and it was a racing story about two pokemon - a Ryhorn and a Kadabra. The Ryhorn ran full-out, but the Kadabra didn't move... until he teleported past the finish line just before Ryhorn could cross. Which enraged Ryhorn so much he started rushing at the crowd.
And, obviously, updated graphics. Considering just how huge that shift was, it's definitely felt. The greater range of movement, the new camera angle, the more dynamic pokemon movements in battle (using Pound on my Froakie actually has him jumping forward and pounding).
So, it all adds up.
I didn't bother getting Black/White 2. But so far, I'm happy with XY.