While I do think the game is fun, I personally find the "fun" weapons (for me stuff like snipers and shotguns) extremely underpowered compared to the SMG's as from my experience, with an SMG (at least the bizon) you can easily get to the first boss and kill them without worry, but with shotguns and snipers there's too little ammo and I would find myself spending almost the same amount of cash on pizza boxes (and health with the issue mentioned later) as upgrades. Also I would like to really suggest making the enemies spawn only after a certain range of the player. I personally find the fact that an enemy can spawn basically right on you and make you loose HP without warning super annoying. CoD zombies has a way to fight this, their zombies have a sizeable delay before they get in the map and are able to attack, not to mention they have ambient noises, which warn the player that a threat is near. This game has no ambient noise and the delay before the enemies start attacking is too small to notice, especially if you're already fighting someone else which leads to the enemies very easily spawning behind you and hurting you without any warning before hand.
This game is fun, don't get me wrong, just a bit unbalanced in my opinion.