I played some more and enjoyed it. I like the variety in enemy design, it's well communicated how each one works, really well done.
What I would have liked to see is some sort of branching levels. Something like a fast route that is hard but super fast, but when you fail that you could still take the alternative route which is easier but a lot slower.
There were again a lot of shards placed in some remote corners and now that I know what they are for I was more motivated to collect them. I think I understand the motivation to place them off the main path, to pose a challenge and encourage exploration. But after getting two upgrades my interest in shards went back to zero as the upgrades where underwhelming. Frankly I did not notice the increase in jump height and run speed. Maybe instead of an increase in jump height give the player a weak double jump instead? I guess you have to keep the upgrades small to not unbalance the game, as you can not predict which upgrades the player will choose. All levels have to be beatable and challenging for all upgrade combinations, right? I imagine this could be a ton of work to balance right.
Maybe it would be a good idea if the shards weren't a currency and instead just gave the player a boost. Either instantly or one the player can spent at will. This way shards of the path would hold the appeal of an investment "Will this detour make me faster in the end?" I think this could open interesting level design options and player choices. The upgrades could then be collectibles in the level. It would not matter as much if the upgrades are insignificant as the investment for the player is smaller. I regretted my upgrade decisions and wished I had spent my hard earned shards on something more effective. If I had just found an upgrade in a level I would have been ecstatic. It would have made me more willing to explore the levels, too. This would have the benefit that you could know which upgrades the player could possibly have at each point of the game, making it less work to balance.
I stopped playing at the 2nd giant encounter. The unskipable cut scene where the giant stands up is just too damn long and I could not endure seeing it one more time. It's ok to make a hard boss, but if you make me suffer through a cut scene instead of letting me back into action as soon as possible, I will be gone quicker then a free steam key on /r/gamedeals