Where to start?
Well you're not at Doom levels yet, I'll say that. The 2.5D (which is what it's called, not 2.8D, and frankly if you claim to have 3/10 of a dimension more than Doom people will get mad at you) is pretty well-done considering you clearly did it purely as an experimental project. Not perfect, but you know, better than I've done.
I would advise you to clutter up the game world some. As it stands the only thing it it are mummies (not zombies), barrels, and a big green circle which I'm not convinced is the horizon for reasons I'll get to in a bit. I can't tell what direction I'm moving in. It seems like you basically programmed it to tween when you move and count down frames until calling a random generator function. I want to see buildings, walls, some kind of indication of movement and more importantly a reason I should are about shooting mummies and defending the zone as opposed to just leaving. I'm not asking for anything spectacular, but throw in a few JPEGs to give a feeling of landscape.
Render mummy corpses. Don't make them disappear until we look away or until after a certain time. There's no entertainment value in shooting at bull's eyes: we want to see bloodied corpses and know we were responsible for destroying the mummy infection. We want to watch our bullets land in flesh and spurt gore. That's why we don't care whether the hero of our mummy game is an asshole who's only looking out for himself.
Again, this is a complaint I'll let slide since it's experimental and not really finished, but it's something to consider for a final project.
This is something I got sick of hearing in my programming classes, but you really have to bug check like crazy. On my third mummy wave a weird thing happened where one of the mummies (or several; they all stack so it's impossible to tell) wouldn't die. At all. He just kept coming at me and I ran out of ammunition. Then, when I was going backwards trying to get away (he was outrunning me) he inexplicably started rendering behind the horizon line even though he was still getting bigger and closer.
And now for nit-picks: like I said, I ran out of ammo after a while. Are there any refills anywhere? Also, add in movement keys other than the arrow keys. Ideally we should be able to map our own movement keys; that way it's less awkward and it can be adapted to a bunch of different control schemes.
You should probably be submitting this to the Newgrounds alpha system where you'd be able to say "this is unfinished and I'm planning on adding things" without getting in trouble.
Again, it's not that I don't like it. I'm actually really hoping to see more from this game and see what it'll be like when it finishes. I've been waiting for a decent first-person shooter and it looks like this could really end up being just that. Really, keep it up, show us more.