Hey pixelwashgame,
I played your game for a bit! First of all, for your first game this looks very good! Overall its a very clean experience, and it feels like a mobile game.
1) The core mechanic is quite fun, but its also very simple. I must say that I think your game fits the mobile genre better than on the pc. I feel like the mechanic of color matching and swiping is more satisfying on a mobile phone.
2) For the difficulty curve, I didn't get past level 3, I always got the message that my water ran out. I tried searching for the tutorial text again but could not find it so I didn't know how to proceed.
3) It feels fair, to be honest I don't know if it is normal, but I could see which color I was supposed to do where before drawing, maybe it was my screen brightness or something? So it felt fair because I could see where each color was supposed to be haha.
4) Didn't interact with it that much so can't really give an opinion here.
5) I think some sort of powerups or something? Maybe you can randomly find these when breaking blocks, which could restore your water somehow, or make you swipe multiple blocks at once.
Anyway for a first game its looking really good, I think you made a very good choice with making something small. Often I hear people making their first game and immediately trying to make a huge game. The game is very good!
Good luck with developing, hopefully this feedback helped somewhat :D