Was disappointed the game just seems to softlock after beating the boss, I wanted to go back and find the last few upgrades :(
Most of the things I felt were missing are fairly minor polish additions that I don't necessarily expect to see in a jam game like control rebinding (mouse3 for the morph ball is an... odd choice and I would've probably liked to change it, though it wasn't a huge issue and I was still able to play through comfortably) or a map screen. I will say that having to check the jam page each time I got an ability was annoying and there should be control prompts in-game - I saw you said you ran out of time to do so "properly" but I don't think it would actually take as much time as you think - just a bit of text that pops up when you get the ability would've been sufficient.
Otherwise this is a very solid entry! It's nothing special to look at but it was a lot of fun to play - it feels really fun to control, very well done. It's also decently large and while I was worried the lack of map might make that a problem, the world was really well designed and I never found myself feeling lost - even with the very minimal visuals you did a good job of making each zone clearly distinct and guiding the player through the map effectively. Also really appreciated the amount of secrets and optional upgrades, it does a lot to cement the metroidvania feel and is something a lot of other jam entries fall a bit flat on.