Pros:

Long and challenging

Cons:

Snow & Rain cause headaches and make you feel very ill

Conclusion:

The snow and rain cause headaches and make you feel very ill after 5 minutes.

I hope you remove the particles in an update, because the outdoor parts are unplayable.

I will change my rating from 9.5 to 10 if the outdoor particles are removed!

Still - this is the coolest thing i've ever seen in Left 4 Dead.