Pretty nice, a little ripetitive, but I guess it comes with the kind of game.
Some ideas:
1) Add upgrades - I suggest "regen" (allows to regen more energy per second), jump (right click makes you jump farther and recharges faster), precision (more damage).
2) More perks (I suggest at least a minor one for every tier of upgrade completed and for every weapon maxed).
3) Damage increase at the end of the upgrades should be more consistent, now it is really poor.
4) Add some music - something epic for bosses and a couple more for standard levels on random rotation.
5) More upgrades for the weapons, and a couple more weapons.
6) More money during higher levels - it would help point 5.
7) Random bonuses during the game - x2 damage, x2 movement, x2 money, stuff like that.
Don't be afraid to make the game too easy, when you have to play a game which repeats the same structure you need to see substantial improvement in your character to feel satisfied.
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Gabri, I am still adding some stuffs. Sso many days doings the particles system and just forgot the WASD! I definitely will add WASD pretty soon!