Tim & Jim

Maybe it was just me, but the collision detection seems very sensitive. In  that there were a number of times I felt like I didn't hit anything and died. Other than that, it is an enjoyable and very satisfying game once you get the hang of it.

When I realized how it works, the game was actually quite fun! It's a nice twist on a physics game concept that could easily be turned into a mobile game or something.

I think the reason it was confusing at first was because it's not immediately clear that touching literally any obstacle causes the climbers to fall through the map. The rocks don't look like hazards, they look like something you should stop at or bounce off of. To a player who doesn't understand the mechanics, it seems like you're falling off the wall at random times.
Something as simple as a particle  effect appearing on the spot where you touched an obstacle, and perhaps an accompanying sound effect, might have been enough to make people less confused about why they fell.