This is a gigantic disappointment compared to the first game.
a.) You killed the atmosphere with the music alone (the first one's wasn't much better). Try putting in some creepy music.
b.) You have limited and useless "upgrades". Try to incorporate the night factor more, and in different ways.
c.) With regards to weapons, once you get to something like the AK, the game becomes a total joke. You need to balance weapons better, and add some different types in (scopes, snipers, grenades, etc.)
d.) The difficulty was super easy in this one. The first game was harder, but not in a good way (just spamming explosives).
Overall, you're one of the few authors who makes great zombie games. I only hope you heed some of the things people post here, because it seems like you're going downhill in terms of quality.