I just started playing AER: Memories of Old which allows your character to transform into a bird and fly around a sky world of islands. I was struck by how good the flight feels in-game. The sense of speed, control, and freedom was immediately satisfying. I've spent most of the game not actually doing what I'm supposed to but just enjoying the ability to swoop, dive, and get from one point to another in a novel way.
It made me curious: what other games are out there in which just the act of moving your player avatar around is engaging, interesting, or fulfilling?