Nice game! Feels good to control, and has some added depth in the form of weapontype-invulnerability.
The weapon rotation did feel a bit slow though - as many have already pointed out - and their damage was a bit too low for the wait. I also found the grenade to be a bit useless and random. I do guess it fits the theme of out of control.
The art style is really nice looking - cartoony and simple to understand. Does a great job at teaching the player - Like it a lot. The sounds also matched the presentation pretty well.
If you were to continue on this game, It would be cool to see some more negative sides to the weapons, like long load time, shrapnel that damages the player, maybe an area effect like poison that harms both the enemies and the player.
Liked the game, great job! :D