Fun, but with a few problems, most of which have been covered by other commenters. To those I would add that the play area is a bit of a strange shape - I would maybe not have stuck to the movie so religiously on that, because if you get cornered with your lawnmower stalled you do not have a lot of options, and your health goes down very rapidly. Maybe a non-lethal melee attack or something to keep them at bay would be another way to solve that issue.
Anyway, with a few tweaks and a bit more juice I think this could be quite an addictive game.