This is a fun and promising game! I think it could be really great with some updates and tweaks! If you do plan on updating this game further, I have some feedback:
1. Switching between ammo types is a liiitle bit annoying to have to do between every shot. Could be nice if there was a way to auto-attack all flagged spaces. How would it know which tier of ammo to use? Maybe right clicking multiple times could cycle the tile through different "tiers" of flag, based on the floor and what types of enemies are on it.
2. The lack of a way to reveal tiles in bulk slows down the game considerably. In minesweeper, you're usually supposed to be able to click the numbers to reveal all adjacent tiles IF the number of adjacent flags is equal to the number on the tile. I can see how that would be a bit complicated here, but maybe my earlier tiered flags suggestion could help with that. Maybe even make it so clicking the numbers auto-attacks the enemies if you have the right tiered ammo? Could be an optional toggle, at least.
3. It would be nice if the number of enemies on the right decreased with each one defeated, so I wouldn't need to count all the v1.0s just to make sure they all add up to 10.
4. Level ups don't really feel impactful. More health is nice, but I tried my best to conserve level ammo because of how it scales with your level, making it by far the most valuable ammo type. I never even used any before reaching the ending, which makes me feel like I hoarded it for no reason. Maybe you could gain new abilities with level-ups, making it easier to clear boards quickly. Then, you could make the game harder by either ramping up the number of enemies, or reducing the amount of ammo, making said abilities feel more necessary, and make it so skillful usage of them is critical to success.
5. The fact that you can misclick on an already-revealed tile, and yet it still wastes ammo, feels bad. Ammo should only be used when revealing new tiles, because there's no situation where shooting a revealed tile is useful or desired. ...I mean, it could be if you got really creative with new, special types of ammo, but all of the ammo in the game is pretty basic, so...
6. I'm not sure why the scroll wheel spams the shoot sound effect, especially because it doesn't actually use ammo or reveal tiles.
All in all, this game has some great potential, and I'd love to see it develop further! I also just wanna say I love the "old Windows" aesthetic, and the midi music adds to it so perfectly!