Nicely done, reminds me of the old Left 4k Dead jam game that Notch made before Minecraft. There are some improvements that could be made to make it a little more involved, because once you figure out how the zombies work, its easy to just make a circle in the main room to corral them around (there's no benefit to exploring at all - in fact, it will likely cause you to get trapped by a horde).
Sound and lighting design are really well done here. You defiantly created a nice "tone" here, which I think is the really important part. I'm sure you had a lot of nice ideas that you didn't have time to implement, as is how these jams go.
Also, super impressed you got a leaderboard working on a game jam game!
Well done!