Interesting concept that was well presented :D
I do think that maybe it’s a bit hard. It did take me about 5 goes to even see the upgrade screen :$, which is a shame because I think your upgrade mechanic is what makes it really interesting :)
If you come back to it, I would be tempted to a) give you an ‘initial’ upgrade at the very start, so players can be introduced to what makes this unique immediately, and b) give the player more health (maybe behind an ‘easy’ mode option, if you think the game is balanced and I’m just too bad at it :D ), or a heal mechanic (blocking slowly increases health?)