According to the readme, this map was originally supposed to be submitted for the second edition of the Maverick Mapping Competition, but somehow never made it in the contest. It is "the 2nd part of the adventure-pack about Dr. Carmack and Mr. Berger", although I have no idea where the first part exists besides InsaneKid's hard drive. Note that there is a short story in the readme as well, telling the time period, location, and characters involved.
The story lets us know that the arena takes place in 1832 on the 13th of December. The aesthetics are mostly true to what you would find in this era, including a custom track which is a loop of Prince Igor - but thematically it does come off as confused. Sometimes I wondered what country I was supposed to be in. At first glance I'm thinking I'm in England, but then I spot cylindrical Kanji lamps hanging off the ceilings. Add to the mix some pictures of "Fear The Undead" which look like advertisements, and overall the arena feels more whimsical than realistic. Then again, maybe this was the author's intention - although with the story that comes with it I wonder what compelled the author to pursue this artistic direction. Maybe he was reading Sherlock Holmes, listening to Turning Japanese, watching Dawn of the Dead, and designing this arena all at the same time, who knows.
Normally I despise symmetrical layouts since they tend to be somewhat boring, but you don't really notice it due to the complexity. Opium is tight and vertical, which will appeal to fans of close-range combat. In addition, the map's speed is increased significantly with the use of teleporters and air tunnels. Both the tunnels and some ladders are unique elements providing some flavor to the arena, but unfortunately the former is marred by the fact that you can occasionally get caught on the light fixtures inside. This issue could have easily been fixed with the non-solid shader property. Besides that, there are other strange quirks, such as wooden guardrails allowing you to move straight through them on one side, but restraining you on the other.
To sum it all up, this map is visually interesting and has okay gameplay, but the problems mentioned earlier will inevitably make it a candidate for deletion soon enough. I advise that the author look into it and give it a bit of tuning so it can reach it's full potential.
Reviewed by EmeraldTiger
Update: The current download contains number of changes and tweaks from the original release. These include; snow, re-worked lights and brushwork, two Shotguns added and some texture changes. 21st Dec, 2011