My idea is that the starter pokemon types be replaced.
Ideas would be:
Psychic, Fighting and Dark.
Electric, Water, Ground.
ETC.
I also think ground should be weak against flying. I like ground pokemon, but they can't hit flying in the majority, and technically should be weak against them. (A soaring bird should take out a ground pokemon, they do to grass!)
Also the abolishment of Normal AND Flying. Why not just flying!? Flying is like normal with wings.... there's no need for normal as well!
Also more dark pokemon, especially ones that have 2 further evolutions!
More COOL-looking dragons, or cross type dragons, such as ICE and dragon... now THAT would be awesome! Ooh! And a dark dragon too!
There should also be an item that can turn certain pokemon into dark by tempting them with darkness... All this would do is make their colour darker/black and make their secondary type dark, with a few dark moves. That'd be cooool.
And my last idea: Some sort of new type that can take out ice or dark or something...
Man, I hate ice...
EDIT: A reply to RLRL. Perhaps when a female/random chance kangaskhan is caught, it carries a baby, that after time, becomes ANOTHER kangaskhan, and also when you breed kangaskhan, the baby has to stay with a normal kangaskhan, and gains xP with it's parent untill like lvl 16 or something.