Pros:

Interesting world, full of well-placed details
Nice weapon placement
Mostly good path design
Nice dialogues (some parts could use some more, but that's personal nitpicking)

Cons:

Way forwards is confusing at times
IMPOSSIBLY unbalanced finale (WAY too many zombies attacking without a break, and it doesn' give you a breather even when the Tank comes)

Conclusion:

Play this until the finale and then abandon it. Seriously. I can only beat it on Easy, and almost always I'm the only one that escapes.