Great job, this was really fun to play!
At first, I didn't realize that you could walk through the gray tiles because I thought they were walls, so the first level was really hard at first, but I figured it out in the end!
Also, I think being able to keep the bullets/grenades and money from previous levels would be fun and encourage strategy from the player.
Other than that, this was a good game! Also, something funny I noticed is that the enemies can kill each other, so I abused that to get past the third level without using the grenade 😅