Pros:

This is the most fun I've had in L4D.  Love the tree especially, hits just the right spot.

Cons:

There's certainly a lot that can be added, but what you've got here works great and is a blast to play.

Conclusion:

Favorite campaign on L4D 1 or 2.  It's true that "bots won't take weapons from the tech tree and that
bots refuse to enter the rocket once it's complete, so they must be killed in order to escape," but the campaign is so much fun that it doesn't deserve points off.  I don't even know if that kind of scripting is possible with what the author has done.