I like the idea of a platformer where you slow down as you collect stuff. Think it's interesting! Reminds me of Skyrim when you overload on loot and then become encumbered. Would've been cool if you could drop the collectibles, maybe even have some puzzles where you need to be slow versus fast to complete them.
If I could give some quick critique, I personally had a lot of trouble distinguishing between what was in the background and what was in the foreground. When I first started, I was a bit startled plummeting to the bottom of the map. Regardless, keep it up! Think the concept is super interesting!