Sandmites are kinda too hard - they are fast, they spawn really close and they have collisions (problem is that they can just stop you from moving away and deal a lot of damage). I think it would be nice to have little invulnerability time after last hit (because it can stack from one mite) and dodge cooldown timer (so you can see when you can dodge). And I don't think collisions on seaweed on bottom of level are needed - it's really easy to just stuck there.
Around 2:30 my game just significantly drops FPS and become unplayable, so I can't finish it.
Game just needs some polish, like upgrades for gun and rebalance of enemies (make sandmites less strong and other enemies more strong), otherwise it's nice.