Definitely 4th gen was overall the worst in my opinion, but still really really good games. With the 5th I'm hoping they branch out to stranger type combos, I'd love to see some super contradictions going on like Fire/Grass or Fire/Ice haha oh and more animal based pokemon.
Really? I thought besides the bad Pokemon Gen IV was really good. It took all the new stuff from the third gen (Natures/Abilities/EVs) and made it way less of a hassle to work with. Third gen is horrible to breed and train in unless you have a lot of good Pokes and are RNG abusing in Emerald or something. Firered and Leafgreen are completely worthless* (Your bike is HALF SPEED WTF), and Ruby and Sapphire are borderline worthless too due to lack of moves and diversity (Oh, and the fact that Lati@s automatically have crap IVs) and lack of Wireless. PS I hate Gen III.
What they really need to start with is a way to solve the broken environment they created in the 4th Gen. I don't know if there is going to be another type, but there needs to be something else that can handle Dragons. Giving them two of the most Powerful moves in the game (Outrage / Draco Meteor), having them only be resisted by 1 type, giving them the stats to run destructive mixed sets, and giving them a great stat up move makes the metagame heavily focused on Dragons and Steels (Counters most dragons). Stealth Rock destroyed a ton of Pokemon, and there are very few Rapid Spin users (Needed a Rapid Spin tutor for HG/SS but all we mostly got garbage).
I think overall the Physical/Special split was a good thing. It made so much more stuff playable, but I think next gen needs some things to tone down the dominance of certain things in Gen IV.
Are there any animals Pokemon hasn't covered? Well, the answer is yes, because I've been through that game, lol. I'll have to make a top 5 list of animals that need to get into Pokemons for the next gen. Another good list would be most essential evolutions, because I have the feeling the new one will be a lot like Gen IV with many prevos and new evos.
*The only useful thing about them is stationary birds, but of course you can't even use Synchronize, so it's a horrible save reset battle against an unpredictable RNG