I dig the way the movement works. Feels almost like it could be rage game-y (kind of is with the sun, haha) or would potentially work really well on mobile.
The sun mechanic is a bit extreme I think. It's an interesting idea, and being able to cling to a wall or just sit while it passes can work okay, but several times I just found myself a bit confused when the sun would go away and I was back at the bottom.
Overall, interesting mechanics and what feels like a good base to expand on. Great work!