Everything!
I love the resorts and having many options, the fact that I don't have to budget for a room, the kitchens so I can bring leftovers back from restaurants and reheat them or cook if I so choose, laundry facilities so I don't have to go digging for quarters when my kids dirty their 6th outfits in 2 days or so we can pack lighter, whirlpool tubs ('nuf said), relaxing more when I'm at WDW because we'll be coming back and we have such a nice place to stay, pool hopping....and that DVC gives the trip planning monster in me a way to stay occupied!
Oh and I forgot....the great bunch of fellow members here on the DIS!
I'm sure there are other things....like that cool feeling from knowing we own a tiny little piece of WDW!