Love getting to make all of the decisions with no arguments and/or whining (well, I occasionally whine, but since I'm whining to literally no one, there's no one to get mad about it). If I want Dumbos, I ride Dumbos. If I want high tea at the GF, I get high tea.
Don't love that as comfortable as I am at WDW, there are still some things I don't really want to do alone. So, I end up wanting to go to the Adventurer's Club, but not wanting to go alone. Actually, the AC is the only club I've ever been to on PI, because on my one and only trip there, it was late and my friend was on some serious "no drinky, but knocks you out without it, anyway" medication. We probably shouldn't have gone at all. Similarly, I have not eaten at 50s Primetime Cafe because I don't want to eat there alone. I've been dying to go there, too.
ETA: I almost forgot, another thing I don't love- knowing that unless I borrow someone else's spouse and children, I may never get to be one of the opening families.