Very promising game. It's quite punishing, though the quicker runs make up for it. I was barely able to complete level 1, but I had a decent time doing it. The thing that puts me off are how quickly one dies to circumstances outside their control - touching the dark pits instakills with no warning, and the quick w-face darkness wisps pretty much instakill as well with only very slight warning. You have to play very, very cautiously around darkness wells, which is fun, until you let your guard down and lose the entire run immediately.
The upgrade system is also fun - by having to actively seek out upgrades and pay for them, there can be a sort of grind to go to a well one doesn't have the strength to beat yet and get shards, then buy the proper upgrades to beat it. I think the time to kill should be lower and slower, however, to minimize seemingly random deaths.
Another note - please make darkness wells easier to find past the initial arrows upon spawning! Perhaps a button that, when held, shows those arrows again?
Overall, great game, and I see plenty of potential. I couldn't get very far because I disliked the quick deaths, but that's just me.