The art in this game is very cute and very well executed!
I think the movement and projectile speed in this game should be higher, it feels too slow and sluggish, every time I want to go across the river I feel like I'm just dragging my frog along which is less fun than it could be.
A bit more enemy variety and having pressure (more dangerous / frequent enemies) increase the longer the players play would have really benefited the design of this game. When you let players keep playing endlessly, I think it's a good rule of thumb to make sure they stop playing because of an obstacle and not because they are eventually done doing the exact same thing with no way to possibly fail.
The lack of sound is a bit of a shame, I would love to hear what those bugs dying would sound like as right now killing them is a bit unsatisfying.
It's a very simple shmup but it's still a pretty good time, don't have people to try this in co-op so can't comment on that aspect.