The over-world is full of stuff to find and mini-dungeons and whatnot if you take the time to explore. The big open fields themselves are barren, but I'm pretty sure that's the point: they're just places to race your horse around for fun. As has been stated, I think Twilight Princess is gameplay-wise (lets forget graphics) an improvement/refinement over all previous Zelda titles *except* when it comes to NPCs, where it was sorely lacking. I'd be happy to have lost a dungeon and in exchange seen more random over-world NPCs to interact with and do quests for and whatnot, but I'm sure a lot of people would disagree...