Pros:

- Custom models, sounds, music
- Long campaign
- Not too bad design

Cons:

- Very bad performance !!! expecially with fire, smoke and other effects it makes the game very exhausting for the eyes
- Some sounds are really annoying, like the shell casting of the custom handguns
- Buggy mechanics (the elevator, a car that I got to but I couldn't finish)
- Puzzles sometimes not presented at all, they're mostly guess work
- Excessive use of keys
- Bad navigation for bots and zombies
- Too long maps, divide them, maybe it will also improve performance
- Confusing textures (I died at the big locomotive elevator beeing confused about what column is the ladder one)
- The boat at the end of a map is flying and it's also confusing when it goes streight into the wall when the tank comes... we were unsure if we'd have to jump from the boat or try to stay in the boat.

Conclusion:

It's a interesting campaign... I'd play it until the end but the bad performance, the numerous glitches and the truck that didn't do anything when I closed the door made me quit,
I'll be waiting for the final version, hopefully you'll at least fix the performance issue.

I've rated it 4 because it's barely finishable.