Had a blast playing it. Simple but fun!

Cheers!

Using time to buy upgrades is a really cool feature! I'm honestly surprised I haven't seen this before. Not going to delve too much into suggestions here as stuff like balancing issues (bullet count being the superior upgrade), lack of enemy variety, and the boss bullets being the same colour as the player's have already been mentioned, but I will say adding a volume limiter to the audio should take priority over anything else. The gameplay's fun and all, but the crackling of twenty ships dying at the same time takes away from the experience. Anyway, you got a good foundation going here, so best of luck if you're continuing the project after the jam. Keep it up!

Liked the visuals for the enemies and the player but their needed to be a different colored bullet for the enemy to better differentiate between the two bullets. 

The first 5 waves require you to move to hunt down the enemies as you don't have the spread to hit them from a far. But after Wave 5 you can just hide in a corner and spam the shot button because by now there are so many enemies and you shot tons of bullets you don't have to aim. This could be fixed by adding a enemy that moves towards the player and deals high damage upon impact making so that the player has to move around  or changing the upgrades so that the player does not shot more bullets but rather more deadly bullets. This would require the player to move around and get closer to the enemies in order to hit the fast moving enemies. 

Boss was good as it required you to be out of the corner but the fact that the Boss does not move makes really easy to get down it's pattern. This could be changed by copying the movement system used on the enemies  and just making it slower. You could also have the the boss spawn in enemies as it increases the number of bullets it shoots. Additionally I would change it so the player does not get life points from lowering the boss's hp to a certain but rather spawned in enemies.

I know this is a lot and you probably could not implement this stuff do to the time restrictions.

Needless to say I really liked the smooth gameplay but there could still be improvements made. 

Very fun, intuitive and smooth controls.

It's a bit of a shame that the enemies are not very tough, and except for the boss don't have the range to be very difficult to beat. It would have been to cool to see more diverse enemies. 

The upgrade system was easy to understand but very effective and satisfying, nice job :) 

This is a fast-paced and fun game to play with a nifty upgrade system. Personally, I think it would be better if the final boss' projectiles were of a different color so that it would be more visible. But other then that I enjoyed playing this game!

The game was fun to play.

I did find that an easy way to win was to just upgrade the shots and sit in a corner shooting everything.

That said I liked the concept of time as both health and a currency, really makes you think if you should get that upgrade or if it'll cost you your life next round.

Good job!

Was a quick, but fun game! I liked the upgrades