I think you can fix the jump by having a minimum jump height when you press the jump button instead of having it completely depend on the input time. If you tap jump, player jumps a fixed x units, but if you hold it they gain a little more height. The problem is that every jump felt completely different to me and it was really hard to navigate all the platforming challenges.
The combat was fun, but the enemies didnt respawn so I barely got to enjoy it. 90% of my time was spent trying not to get killed by the spikes (and failing)
As for the main upgrade mechanic, I like it BUT I managed to softlock myself from being able to kill the 4th boss. I got glass cannon and gave the enemy the thorns skill which resulted in me always killing myself after landing a few hits on the boss. The one healing item in the arena wasn’t enough to save me :(
Overall solid foundation for a game here. The graphics, music, sfx, and especially the voice acting are all great. Fix the feel of the platforming, add some more content, and you’re set.