Side Quests and Mini-Games. We've already got a thread like this, but I'll post anyway so as not to be kicked off for rent-a-modding.
I liked the figurine and kinstone sidequests in Minish Cap. They kept me occupied for a while, and that's a good thing for me who gets bored if I sit around for more than about a minute. I also thought the item trading thing in Link's Awakening was kind of cool. You had to find every character in the game and trade with them in a certain sequence or you can't beat the game.