Great game! It actually reminds me of my own entry to this game jam. Restarting the game to get better got really addicting. I love that you can shoot through multiple enemies and explode the grass, it adds some strategy to the combat.
If you want to expand on this, I would add more enemy types instead of spawning larger quantities of the same enemy. For example, after a while you could start again with a few enemies, but have them move slower, or shoot bullets at you.
You should also add some kind of score system, so that players can better estimate their progress.
Overall, great job!