Pros:

Clean Looking
Smooth level design
Nice flow
Funny jokes and music

Cons:

Zombies spawning in plain sight
Buggy AI (Is this AI issue, or developer issue?)
Buggy "Lift" in Act 2 I believe
Poor Game Instructor

Conclusion:

Very challenging (even at normal) and engaging. Group had a fun time playing through this, and we really had to work together to get through. Taking a break between Acts 2 and 3 for sleep, then will play through the rest some other time. 
Edit: Played through acts 3 and 4 tonight with my buddies, and the acts were absolutely horrible. Act 3 was incredibly short and just consisted of a lot of back-tracking, and act 4 was nigh-impossible to complete with 4 competent players on normal. The game instructor simply said "Go to the rescue point," but failed to indicate where that was. 3 consecutive tanks quickly made mincemeat of my team as we attempted to figure out where, in this huge complex of tents, "rescue" might have been. This map needs work, and play testing. Lots of play testing.