Hrmmm, I hate to say this, as I'm typically a fan of these games, but I just found this experience to be quite boring and lacking any sort of interesting hook or escalation. Yes, the characters and story are very quirky and amusing, the artwork is quite charming with a lot of cute easter eggs, it's neat that you were able to setup this old-school Wolf3D-esque gameplay, I liked the spooky pitter-patter of the zombies as they get closer, and so on, but I just wasn't having any fun: a real style over substance situation, unfortunately.
There were just so many things that didn't feel right to me that led to this really tiresome and bland feeling:
*For example, when a game about delivering pizzas makes it so that the act of delivering has no fanfare or feedback to the point where I wasn't even sure whether I delivered anything since all they do is just shuffle the box, you're really starting off bad.
*You've got a decent variety of enemies, but they're all functionally the same and don't encourage any sort of interesting new strategies of play: you can easily shoot them or just plain ignore them. I really got my hopes up for the stalker enemy thinking they'd be something cool like Nemesis, but no dice.
*Speaking of shooting, it felt very unsatisfying and pointless despite there being some good flinching/dying animations. In theory those animations should've helped give satisfying feedback, but there was just something missing that caused a lack of connection for me.
*It didn't help either that you stay in the same level the entire game, which is not only incredibly small and thus easy to feel like you're just running laps and delivering to the same locations over and over, but has tons of weird annoyances like being unable to walk over a fallen-over fence and a flat-on-the-ground stop sign.
*I also didn't know why there was this system of restocking pizzas back at the base, but they seem infinite, so why is this busy work even here?
As I was playing this, I was just under the assumption that this was some sort of sacrificial test game for your first foray into 3D FPS design: hoping that's the case and we get something cooler in the future by working from this.