Some Pokemon could use improving. When people say leave the first Gen Pokemon, they don't actually realize they are including Eevee. Eevee deserves some more evo's.
EDIT: Also, I really want to see more Dragon and Ghost Types. Also, perhaps some extra Ice types. There isn't enough of them. For Dragon, you should keep the rarity, but Ghost types need a real bulk on their numbers. I think there's 13 Ghost Pokemon. Really? That's really quite bad. Ghost's are so rare in the game, and I feel that they should be more common. Especially at night time. They need the Pokemon only appear at night/day thing. It really helps.