I found Rog Castle empty, no zombies with a lee enfield. I felt lucky because I just started, but when I went down the stairs, fell off them and landed on the other side of the room and died. Now every time I see a Lee Enfield I think of bad juju.
This would make sense. The kind you are talking about are just called Infected, its a human caught in between human and zombie. The infection is causing their physical levels to increase. I think they should be able to be taken down in one shot, but then they wake up as zombies so this would be a great place to add the whole 'double tap' thing. Anyway this is a good idea.
I kinda like it, not being able to see unless you have a flashlight out. What me and my friend do when its dark though is just go to another server, not all of the servers are dark.