I think the graphics look great. The "less flattering" aspects of the overworld simply remind me of the scaled-back look many JRPG overworlds have -- perfectly serviceable, and frankly still more immersive and interesting than the series to date.
But what really steals the show are the battles. Those look perfect, imo. Seeing old Pokemon in that style was really reassuring; it shows that all the charm and nuance of the sprites carries over into cel-shaded polygonal 3D. Golurk, Mienfoo, Ralts, Psyduck -- they all look great. And seeing the starters in action was a real treat.
I'm at the office now, though, and I can't recall -- did they show Chespin in action in the trailer?