Very cool seeing the swarm tearing the landscape apart as they move. Sound design was cool but the gunshots got quite abrasive after some time, also I think adding a rapid fire mode would work well as it can get tedious clicking over and over.
The swarm is pretty intimidating, I think it would add a lot if you attached some audio to each enemy so you could hear them skittering around you.
Overall, great physics effects, very intimidating atmosphere, World War Z vibes, I dig it.