Stunning, atmospheric, a rare gem. Difficult and daunting at first, but well worth the challenge.

I felt it was about time I wrote this review for you! 

TLDR- Here are the highlights of my review.

Pros:
A deep, dark journey into an ancient castle riddled with secrets and traps.
A large emphasis on clue-finding and paying close attention to your surroundings.
The player is rewarded for going off the beaten path with unique melee weapons as well as supplies.
The environments are beautifully detailed and full of variety
Teamwork is heavily recommended, so bring some friends to fully enjoy this experience.
Supplies are spaced out so you don't feel like you are drowning in throwaway items.
Features custom music and ambience, unique models and other eye-candy.
A long campaign with plenty of variety, challenges and unique content.

Cons:(Most of these cons are alleviated after becoming familiar with the map)
This map may not be easy to complete on the first attempt, it's easy to fall prey to deathtraps that you aren't expecting.
The lack of ammo piles means that players can chew through ammo and be unprepared for tank events.
If English is not your first language, you may struggle to understand the clues to certain puzzles.
Playing this map solo is doable but not recommended for beginners, unless you are already familiar with the puzzles, ai survivors will often be downed by environmental hazards they failed to avoid, and a poorly placed SI can end your run in an instant.

Recommended difficulty: Easy-Normal (Solo) Normal-Expert (Team)

My experience with this campaign was staggered between multiple unfinished attempts until I finally managed to sit down and play from beginning to end with a team of players online. My love for this campaign's atmosphere kept drawing me back into it and I spent a great deal of time exploring the nooks and crannies of every mission, discovering a plethora of secrets that were carefully placed and satisfying to discover after much rigorous searching. This map has alot to offer for all soughts of players and I felt like the adventuring through a dark and imposing lair was immersive and exciting without feeling like the setting had overstayed its welcome. 
 
The Castle of Lazar feels as big as it looks from the offset, the creator has crafted an intricate world full of challenges in the form of zombie events, interactive puzzles that test your observational skills and journals that set the tone for the overarching story of the area. It's enjoyable to take your time and read through the journals that record events occurring behind the scenes that give a narrative tangent to the typical custom campaign, which follows a complex and multi-faceted timeline of events shown by multiple points of view. What the author has done with the tools they had available to them is nothing short of exceptional. 

Honestly, this campaign should be commended for doing something unique from other popular custom campaign styles, it's extremely difficult to pull off such an intricate l4d2 experience that can draw you in by its unique story-telling, puzzle-solving style and yet still feel like a worthy addition to the zombie-slaying game. It's by far no means a perfect gameplay experience as the first few attempts may be difficult at first, and the puzzles can block progress and leave you feeling stumped, but once you understand how the map thinks it becomes increasingly easy to adore its uniqueness. 

Personally I love playing through this map with some medieval/horror themed mods. You have really made something special here Derecksena, I hope I will get to experience more of your stuff in the future..