Hey, this game is surprisingly good! There are several issues though:
Improper aspect ratio on widescreen monitors: the aspect
argument of the d3d_set_projection_ext function (which you should use) will change this, you'll want to set it to (display_get_width() / display_get_height() )
Sort of related to the above, the resolution appears to just be pre-defined (800x600?) stretched out over the desktop resolution, you should either let it stay at the players desktop resolution or have a set of options.
You can use views in rooms using 3d projection, the port size is the resolution output to the screen.
Low field of view, it's very zoomed-in which makes zombies at the edges of your vision harder to detect (I notice you consider this a problem since you have the HUD indicating zombie positions
) and causes nausea, increase this by changing the angle
argument of the projection_ext function to something larger (I'd say at least 75).
If you happen to get surrounded by zombies before noticing them you'll die ridiculously quickly, I guess each zombie adds its own damage as they get close.. you could limit it to let only a certain number of zombies can attack at a time so you won't die quite as suddenly and unpreventably.
There's a pretty cool bug with the shotgun: if you run out of ammo and switch to pistol and back, the ammo will turn into something like -12/0 and you can shoot, without need for ammo, as fast as you can click. I still can't survive for very long though, as the aforementioned sudden group attack gets me every time
I like the feel of the weapons and the sense of impact when you hit, and you have very good sound as well. You should probably use 3d sound though, at least for the barriers-breaking sound, since it would let the player hear which barrier is being broken.
oh and there's an error about a non-existing surface if you try to exit to menu at any graphics setting other than "fancy"... and if you move the window away from the centre of the screen in windowed mode the cursor will still be locked to the centre making you click outside the window when you want to shoot... and the zombies have a very funny walk when they've just spawned. I keep finding more and more problems, not giving you a break
I do it because I like the game though!
Eurgh this post turned out to be a wall of text