I spent way too long trying to kill the mosquitoes at the beginning before eventually beating the game and figuring out why they were invincible, haha. Clever, clever. It did feel pretty strange that the first big boss guy died so fast though because of that.
The attack animation was good and it was easy to tell where you were going to hit, and the player character controlled well enough, but as I'm sure you already know, having walk cycles/jump animations/etc would make everything feel a lot better. Upward / downward slashes would also be really nice for some of these combat situations. Just food for thought if you keep going with this; lot of potential here!
The monsters looked phenomenal, really grotesque and disgusting in a good way. It was fun getting to choose upgrades and the ending was great.