I liked it, the loop is pretty good but still needs some tweaks in my opinion:
- I'm not convinced on limited ammo, especially if the recharge is very slow and the pace requires quick reflexes: it ruins a bit the fun and leads to frustration in the end
- Shift/RMB to boost: the fact that the spaceship follows the mouse cursor and not the direction I'm moving to with WASD is a bit counter-intuitive, I think it would be better if it follows the WASD input
- Some enemies and their projectiles are ridiculously small, sometimes I struggled to see them at all and I was inevitably hit: I don't know if you have already decided the art style of the game, but I would suggest to increase their sizes and maybe add some glow/contour around them
- Also: player hurtbox feels a bit too big sometimes
I hope I wasn't too harsh, that's just my opinion after a 15 minutes play. The upgrades are cool and well thought and the waves seem to have good economy balance. Keep up the good work!
PS: in the tutorial there is no way to know how many "gold" you have for your upgrades, might I suggest to add it?