Definitely the game I've played the longest in the entire Jam. At first I had some problems in some rounds, and zombies kept really close. Then I found out there's more than just the "Gun" menu. Gosh what a discovery, grenades, health, I just overpowered myself and the game was way easier from then on. Thanks for the auto-reload feature, a lot! But zombies started to keep improving too... although not that much. Grenades are way too powerful and cheap :D
Eventually the game froze at some point :( There was a zombie left which simply stopped moving and I couldn't shoot it either. Grenades couldn't hit it, so I guess that was the endgame for me. Let's call it the Super Zombie xD
About the game itself: incredibly great and enjoyable. Graphics are really cool, minecraftesque, but it has too much bloom. Heck, I've just been under eye surgery a week ago and have flares but this was definitely not the case ! xD. Sound is good and feedback and bullet/gun animation is great. Excellent work with the upgrades and the difficulty curve (except grenades, at least up until I played)
EDIT: Sorry, I just played the original version without further reading, so you may ignore the bloom and the round 33 problem :)