Not too bad of a game, but I've had a few problems with it ...
the game feels horrible, in top down shooters like this one it matters alot, the complete lack of animations apart from particles makes this game feel kinda bland, not to mention the weapon changing -which poses the game- is breaking the little action this game has.
The way melee works is not explained anywhere AND is glitched : there's a cooldown only for hitting the same zombie, if you find yourself stuck between two zombies just tap left and right and they should be dead in no time !
Speaking of glitch, this one is of the unconvenient type, I once started a level between 2 bosses, which got me stuck and instakilled.
Apart from that, money balance is mediocre at best, some weapon upgrades barely changing anything to the weapon and some useful one increased by a ridiculous amount !
So yeah, even if I apreciate the ZQSD option, there is still ALOT lacking to make this a good game, unfortunately.