nice atmosphere, I agree to @WILDMUSTANGX about the jittery jumping behavior.
Maybe you are using a direct jump control (something like "On Space" press?)? I would recommend - for this is a slow game - To use simultaneously ("On Space" or "On space down") -> set a boolean "demandJump" to true and use it to execute the jump (if demandjump == true , ...), and hold it true until "On release Space" with a while loop. This way your code will not miss a players wish to jump when he presses and holds spacebar for a bit.