This is fantastic! The music really sold the idea of a heroic slime adventure. The sound effects were cute and gave me a real attachment to what was effectively a blob with a crown. The graphics and overall aesthetic gave me early Crash Bandicoot vibes, which I loved.
Perhaps this was just me, but it took me a while to work out that I didn't need to be on the ground to fling myself, and then it took me even longer to work out that I was actually sticking to the background wall; before that, I thought I'd hit a bug every time it didn't let me do it.
I found the slime blobs a little finicky to pick up sometimes, so I would have liked the hitboxes on those to be a little more generous. I also felt that a maximum fling could have done with a little more power, but perhaps that would have thrown the balance of the game off.
I was a little disappointed when all I found at the end was endless black screen. I started trying to work my way backwards through the stage until I hit the control bug others have mentioned and decided to quit.
Overall my criticisms are mostly nitpicking; I absolutely adored this game! Everyone on the team should be very proud!