Really interesting game! I liked the idea and the FTL style encounter chooser, though i was a little unsure of what each of the icons were till I got to them . The combat is interesting, I wasn't expecting the left mouse button to be movement,  with such a fast movement speed of you and the zombies, I thought that a WSAD scheme with the ability to shoot while running would be more appropriate, but if you were to tone down the movement of you and the zombies, and also remove their ranged attacks, then having to stop and shoot will be much more intense! :D 
The tall zombie with the buzz saws was a little bit of a bullet sponge, and was more irritating to fight than fun, the first stage of the game was very difficult for that one reason, thankyou for the regenerating health! 

The normal zombies were cool! the ranged attack ones were a little strange to me, but I get the need to keep the player moving and dodging, I think you may be able to get a similar style with melee only zombies and a slower stop and pop shooting style. 

The puzzles in the train yard were cool! no zombies followed me in there, but I imagine it'd be tough trying to juggle shooting the undead and trying to solve the pipe or switch puzzle. 

Great game!