from the audio of the Combine soldiers, headcrabs and
various zombie enemies, the ground pounders and the antelions etc to the great use of lighting.
-- test your strength against
zombies, soldiers, cyborgs, mutant, cannibals, mechanical dogs, drones... — get engaged in several unique boss fights — complete special missions with
various enemy types to gain experience CHALLENGE YOUR FRIENDS — You can face the
enemy alone, but you won't last long.