See this is a good mod in theory but in action alot of it falls apart, which is a shame because most of it isn't the designer's fault.
For starters the fact that the zombies can't climb robs the game of all tension, considering you can just sit on a car or box and just pick them all off with your secondary weapon, but then there's also the odd occasion where they can still climb surfaces like chainlink fences, ladders, and drainpipes (which does make sense, though I don't know if this was designer oversight, intentional, or just has something to do with the game's coding)
The headshots only aspect makes this a tremendous pain in the ass to play considering the hitboxes for the infecteds' heads are so piss poor. You can sit there and unload into a zombie's face point blank with a shotgun for 5 minutes and get no results.
And don't get me started on the riot zombies. These things went from being a minor inconvenience to being a royal pain in the friggin ass. Considering you HAVE to hit them in the back of the head which is such a small area, and then there's the hitbox issue again.
Then there's the zombie speed, which totally takes away all threat from them unless they mob you in a tight area, or get you from behind which is really unlikely to happen unless you stand in one place all day like a moron.
I'd gripe about the "I ♥♥♥♥ my pants just now" walk but I know its not the designer's fault since valve never really added an aggressive walking animation to the infected.
All in all this mod has alot of potential but unfortunately its just for the wrong game.