Very solid entry for your first submitted project. I think that you have chosen a good type of a game in order to put in quite a lot of content. Few suggestion for the future (or a post jam version):
- make it bit more challenging - you have pletny of enemies already but it still lacks bit more "juice". You can easily add smaller/bigger types of enemies. You can even make certain type of enemies come from the right... this way you'll make player to be more active
- part of the challenge could be also fasten up the speed
- player could have different types of shots
- screenshake - is simple yet powerfull effect to juice your game
These are really just a suggestions that I can see, would make this game, bit better, but overall you did really great job! I see that there are also few things to polish, like stop the motion of an object after it is destroyed, as you can now see the score moving. These are really barelly a complaints as your game feels truly good for a jam game! Keep it up and thanks for your game! Good job