The only pokemon I don't like in Gen 5 is Trubbish and Garbodor, I could come up with better pokemon than that mutated thing and Oshawott looks funny, but oh well 4 Oshawott, he's ok
Rivals who either don't assume Ash is weak or Rivals who think he's weak then get the crap beat out of them in the next battle, instead of Ash losing most of the time.
And better pokemon of course, u know better pokemon every generation right ?
Aged/Older Ash.
Etc. (can't think of the other(s) now)