Impressive work! A Wizz mentioned, there isn't a lot of collecting, but the shooting is very solid.
Enemies explode in a very crunchy and satisfying sound, it has really good game feel. Also impressive that you managed to include a Versus mode - I couldn't test it much but it seemed to work fine.
Just some quick constructive feedback:
- Try to make the gun autofire instead of firing per each click (this also serves to regulate attack speed)
- Give some invulnerability frames after being hit to avoid insta dying when an enemy hits you
- Add more powerups that affect the gameplay to keep it varied.
- While the Versus mode was interesting, working on the main game could have been a better use of time (unless you wanted to learn about developing versus mode specifically)
Great job!