My thoughts on X and Y summed up in a single statement: There are no brakes on this hype train. It just doesn't stop.
I loves me some Pokémon; I own every main game in the series, as well as most of the spinoffs. X and Y are not going to be exceptions. I'm super excited, because this next generation is really going to mix things up. They're introducing a new type for the first time since Gold and Silver. Fairy-type is gonna throw things out of whack, since it's effective against some of the most commonly-seen types in the metagame, being super effective on Dragon, Dark and Fighting, resistant to Fighting, Dark and Bug AND immune Dragon. It's also weak to two of the least-commonly seen offensive types, those being Poison and Steel. Fire, Steel and Poison resist it, as well, and while Steel didn't need a defensive buff, Poison and Fire certainly did.
A lot of the new Pokémon look awesome, especially the Fire-types. Fennekin is cool, but Talonflame and Pyroar are awesome. Gogoat is really cool, too, and so is Clauncher. I could go on, but you get the idea.
Mega Evolution is a pretty awesome idea. My only concern is that many Pokémon that don't need a Mega Evolution are getting one. Garchomp especially. That thing was too good before; it doesn't need to be any better. My prediction is that Mega Garchomp is gonna murder everything just by looking at it funny... But, the thing is, it comes at a price: Mega Pokémon have to sacrifice their hold item, as they need to hold their respective Mega Stone to Mega Evolve. Hopefully that ends up balancing them.
Last but certainly not least, character customization, finally! I don't really like the player characters' starting outfit, actually, and while ones from other games are alright (I particularly like Hilda's design, and Rosa's kinda grew on me), character customization would just make everything so much more... personal, y'know? (Before anyone asks, yes, I am male and I play as the female characters. Don't judge, man.)