I liked most of this quest, it had some rather exciting exploration with several neat areas. And I especially dig that most things are fairly non-linear.
I've got a couple of nitpicks and/or suggestions for things that could maybe be improved if you wish:
- I used one of my earlier keys to get to the merchant selling the bug catching net. This left me lacking when I eventually found the path towards the lamp. But because of my lack of lamp I never noticed the screen transition I needed to pass in order to find the screen with the final key. It was a bit mildly frustrating because I just ran around feeling like I had wasted a key.
- A fairy fountain or something at least midway through the game would make sense. The bug catching net in general feels like a useless purchase since you need to kinda of hope for a fairy to drop from an enemy; while also being both ready to scope it up before you pick it up, all while praying it does not camp inside of a wall. I caught a grand total of a single fairy with it in my playthrough, which wasn't worth the asking price. So a fountain somewhere later on feels like it'd be good.
- The warp tiles in the green caves are a bit unclear where they will take you. It felt a bit like trial and error figuring things out, all while hoping I didn't step on something that would send me backwards rather than forwards.
- The smoke/mist making the trees spam fireballs at you wasn't especially clear. I know there is a hint for it, but I got to the NPC with that hint well after I had cleared most of the area.
- Speaking of which, some of the projectile spam is maybe a bit too intense? Those trees could shoot half as many bullets and they would still be intense.
- The ending was a bit abrupt. I was expecting a couple of more screens or something. Or at least stepping up above ground before it cut to black.
- The water drown respawn locations let you cut certain corners; allowing for sequence breaks. (This is how I bypassed the keyblock right before the lamp).