Leveling for sure! Being able to grow stronger, especially when it expands the world you can reach, makes me want to keep going. The beautiful cycle that always needs skills or something to keep me around. The numbers are nice, but getting a new ability at a certain level is something I always look forward to.
Agreed! Story with little pieces missing is the best kind. I get so bored just following the line. I'm very piece-of-candy, so I love when there's little mysteries to figure out, especially when they impact the ending, or even better, the current world as is. Though, it's easy to tell when a game's just giving you fetch quests to extend playtime.
So unlocking skills/spells is always enjoyable, especially when it's linked to levels, BUT... What if you unlocked special hidden spells and skills by doing certain things? Like taming 1000 wolves unlocks a special spell to transform into a wolf or summon a greater version??
I'm interested in ANY more ideas you have!