Pros:

Building stuff
Hilarious
Constantly pressured
Easy to pick up
Very fun

Cons:

That darned tutorial button close to start button
Things can end up underground (adds to the hilarity :D )
Zombies teleport spawn instead of running in from outside

Conclusion:

This is a fantastic map. I play the sandbox survival with my friends for hours. It's got a great difficulty and the number of options have us still looking for a good build order. The best map I've played since LOTR helms deep