Pros:

-Very nice design for a first map
-Interesting atmosphere
-Good use of models/decals
-Good survivor nav

Cons:

-Not very many infected
-SI nav is basically broken (they dont move or do anything till you get near)
-Very easy
-You can't shoot through some fences
-Not enough ammo dumps
-Finale is a bit boring and overused

Conclusion:

For a first map, its very nice. Since it is a first map, it doeserves no less than 75. However, the nav meshes need a complete overhaul before it is professional. I'm not saying you're bad at mapping, you live and you learn. I would also consider making more maps (maybe form land, to boat, to sea, to oil rig) and then make the rig smaller, and the finale a bit more exciting. Keep mapping, you can only get better.