Firstly, the map seems to start and end way to abrupt. Basically, it feels like you are in a tiny box with a random bar in between. This feels weird to me. Is having two incredibly thick walls around this tiny bar really necessary?

I get that the point may be to show the citizens of Sunny City trying to keep the Zombies from escaping the bar, (I am assuming why this design choice was made) but I feel like a tiny fence would be a lot more sufficient, ascetically pleasing, and realistic.
I love the Jo's Bar map in Zombie Nightmare, and would advocate the Versus map to follow suit. One clear issue with that suggestion however is that individuals could get into places that aren't even visible or reachable to other players.

One solution I have would be something along the lines of a Zombie crawling out of the ground in order to attack the player once they have reached the aforementioned area. That is just a thought though. I have had other ideas such as a nerve gas that slowly kills you and turns you into a zombie, but I am sure others can come up with better ideas to combat that issue. Anyways, I hope @Hjarpe and @Gurt acknowledge my suggestion. If any of you would like to add your opinion feel free.