I like a lot about this concept, like the risk-reward of how greedy to be with having more treasure slowing you down.
I think it would be more interesting if the player knew where the exit was, however, as I found myself just wandering around very very slowly by the end.
Additionally, I like that enemies don't kill you, you just want to avoid them because they're heavy and slow you down a lot. However, if enemies can't harm you, why does being slow matter? I feel like there needs to be some sort of motivator to stay light and fast, like a timer for the level or enemies that you need to run away from or something