I tried all the characters and they seemed pretty different in power level. With the first one I blitzed trough everything and I don't think I even got hit once. She leveled up super fast and became overpowered very quickly. The bomb girl and the healer had interesting attacks but they were also a lot more difficult to use and get kills with consistently. There's also a bug where you attack when you pick a level up and that doesn't matter for most of them but its pretty annoying for the last character because it switches between heal and damage. Oh and occasionally I would start the game without a character, not sure what caused that.
The core gameplay is fun and I like that there are hordes of enemies but the progression was a little weird, at some point in the midgame there weren't a whole lot of them on the screen but then before the boss spawned there were suddenly dozens of them everywhere. The level also gets a little empty after you destroy the barrels, I would like to see some different terrain features or obstacles. Oh yeah and it took me some time to actually find the boss, I know he spawns in the middle but its hard to tell where you are exactly.
I didn't look at the masteries very much, they seemed a little buggy. I couldn't exit the menu once and had to reset.
Other than that, it's pretty fun to play, good work