What feature would you like to see in a new Pokemon game?

I begin: GF, give me a good reason not to evolve some mons. If I don't like an evo, I want to be able to make good use of an unevolved mon (and not with an held Item or with some shady tactics) - I know it makes sense that a Pokemon gets stronger when it evolves but maybe make it not as drastic or give some stats a boosts and some a nerf or something like Pikachu gets a higher initiative than Raichu but Raichu gets the higer Sp.Atk.