The sprites are beautiful, the movement and animations are smooth, the backgrounds are gorgeous and the guns feel amazing.
My only complaint is I wish there was more ammo, or at least more packs around, considering how quickly you can burn through them - the pistol is just nowhere near as fun as the rest of the arsenal. I also wish there were more checkpoints or at least some additional lives like in Eternal ; getting far and having to start over again can be a bit frustrating. By the way, the shooting reaction of the zombie soldiers is also a bit too fast when you're close to them, it makes it hard to kill them without taking damage.
Still, those details are minor compared to the rest of the experience. Kudos!