I agree with Toshiro, it looked as though they only wanted to create a new generation of Pokemon for the sake of sales instead of actually adding some creativity to it.
As much as I looked for cool pokemon, aside from the starters the only decent pokemon I found was luxray. Most pokemon are strange looking and the ones that look like they can stand up to fight have very poor stats.
They have a point to their favour, thought. They introduced new Eeveelutions, which are great but, again, they have poor stats and a lot of weak spots.
So I ended up just bringing my pokemon from Emerald into Diamond, but it sort of bothered me that Ralts now has a new evolution. Not because I don't like it, it actually looks very cool, it's just that I always have a MALE Gardevoir in my party and now it's easier for other trainers to laugh at him.