Hey, thanks for playing and I'm glad the game drew you in even more!
Yes, there's some weird itch-Unity issue going on. When you go to hit fullscreen, there's two fullscreen buttons now, the grey/white button and then the blue button beneath. If you hit the blue one, then the screen scales fully to the window size. Haven't figured out why that's happening yet.
Regarding expanding the game, yup, ammo and more weapon types are on the horizon! I added a cooldown to the handgun too, that was nice and it made things a lot more interesting. The zombies are slow and lumbering, and take a few hits to take down, but they blend in well with the background, so you gotta watch your positioning as you shoot them and even break away and create some distance. Soon I'll add the ability for them to lunge at you, that's gonna making things even more interesting!
Regarding movement speed, did you feel that even the running was slow?