I had some trouble on my first playthrough since I grabbed some ammo before building any towers, and I didn’t have anywhere to dump it (although I realized later that I could have just jumped off the edge I guess).
Once I figure that out, I got managed to get to 7 waves on normal, which was fun! I got caught off guard by some enemies sneaking through my early defenses and breezing through my (lack of) second-half cleanup towers. Nice little game!