I love the fact that you can travel fast - with the running shoes - without having to walk around for about three hours into the game until you finally get the bike! (Red/Blue/Yellow) Yey!
I hate the fact that once you've defeated the elite four + champion, you go back to fight them again, and they act like they've never seen you before! They should at least say: "Hello (name), have you come to fight me again? I wonder if you've got stronger, Champion." There's no respect!