Pretty good but get's boring fast...
Even with the muscle men after a while it got pretty boring...all I'd have to do is place 2 baricades across from each other and stand in between them so I could heal them both at the same time if I ever needed, and whail on the muscle men with the m16 (or what ever it is...it cost $5000). Come out to knife the crawlers, rinse, wash, repeat.
Oh, and adding achievments would be a nice improvement too...^^