I like how it's still called "Sprite Nav v0.x.x". That should be the secretive "development name" until it's released. XD
So, which sounds should be used for the menu? I say pressing "Y" plays #3 (shortened to a few seconds). Afterwards it goes back to 1 or 2, maybe at random.
Let me know if you decide to add some more graphics tiles, or proper animations. I like animating. Even if it's simple stuff like recoil or zombies leaning left and right when they walk it helps it look better.
Does using recreate sprite before updating the screen slow down the game very much?
What about seeing your own feet move?
EDIT: Try replacing "updatescreen" in the timer with:
    LET check = (check * -1) + 1
    IF check = 1 then UPDATESCREEN
    END IF
That updates every other frame, it should be faster. Let me know what you think, and if it looks too choppy or weird. I think it's fast enough though.