The few games that have come out that have actually used Hi-Res images of Pokemon and sprites seem to present the Pokemon we've known before as being very...awkward. An memory comes to mind of when I got Colosseum, being so excited for "3D" Pokemon battling. What came as a disappointment was a lot of the attacks had very weak animations, the Pokemon animations themselves were very minimal and strange, and the Pokemon themselves looked extremely awkward. They didn't really look like Pokemon we came to know through hand-held device games with sprites. This is what I'm most concerned about with the new graphics of X & Y is that with 3D Hi-res Pokemon instead of sprites, battle sequences might not live up to an expectation that 3DS should.
Also, when Pokemon Black and White came out and they experimented a lot with camera angles, it was very fresh, new, and exciting. The game seemed a step higher than most of its very flat and boring predecessors (in terms of graphics), and the slight tilt of the camera instead of a top-down view was a good choice in my opinion. From what I've seen in the previews, it seems these new games will be more of a Third Person Camera Angle, which is radically different than past games. That seems unconventional to me, as I think it would be very hard to get a good idea for what areas look like. Plus, I feel like it will take away from the classic feel that is Pokemon.
Someone mentioned something about blurry backgrounds? Yeah, I noticed that too and it bugs the snot out of me. With more involved games like Kid Icarus and Starfox, the backgrounds don't need to be hugely sophisticated due to a gamer's focus being on what's happening, which is a lot. But in X & Y, if you're just walking around, the blurry background could definitely pull from the quality of the game.
Overall thoughts: Not looking forward to X & Y as much as I did with BnW.