This is a personal, largely spoiler free (or spoiler-vague) review of the Ordo Templi Orientis custom campaign by Mathieu Martin for Arkham Horror the Card Game.
In Ordo Templi Orientis, investigators head to Europe chasing after Dr. Elli Horowitz who is looking for the holy grail. Along the way, they run into Aleister Crowley and his Ordo Templi Orientis cult who has allied with the nazis to obtain mystical power.
The Ordo Templi Orientis campaign suffers from poor wording, unclear effects, and broken scenarios. Right from the very first scenario, there's serious design problems - in Scenario 1, you need to gather and spend clues to draw extra encounter cards, some of which are story assets you're looking for. However, the number of clues you're spending and number of extra cards you're drawing doesn't change based on the number of players - there's even points where the lead investigator will draw extra encounter cards that doesn't account for any scaling, making solo play an absolute nightmare. All these complaints don't even dig into the worst mechanical issue of the scenario in how it handles doom, causing actions to add to it up to the repeatable agenda's limit - which means that if things go wrong, you might only get one or two actions between multiple characters in a turn, but still get enemy attacks and encounter cards as normal.
Unfortunately, there's no scenario that lacks these issues - Scenarios 2, 3, and 4 can all be locked out by spending or losing clues, and there are story assets that can be defeated and prevent completion of the scenario without it being clear how you're supposed to proceed when that happens. There are points where instructions are impossible to complete - in Scenario 2, one card requires you to put an enemy into play at a location specifically if you haven't found that location yet, and put an enemy into play elsewhere if you have - and the flavor makes it clear this is what's meant to be written. Agenda and Act flips suffer the most from these, having instructions that just don't make sense, refer to spawns that already have happened, and more.
Even if you can somehow get through all of this and mind caulk over the set-up issues, the pay-off isn't worth it. The story is paper thin - which wouldn't be a problem if it didn't spend far too long on descriptive text, only for your investigators to decide where to go next based on stumbling on and overhearing someone by chance. It needs to be called out, too, how bizarre and insulting it is for your characters to head to France, only to be attacked by "Lady of the Night" enemies that you're encouraged to kill. Even when they are functioning, the mechanics of the scenarios aren't worth it either - there's one scenario that involves searching in 20 locations, 17 of which are identical identical to try to find the one that matters (which might not even be in play, ever, and you have no control over!), or dealing with encounter cards that force all players to draw an enemy, quickly flooding the board and overwhelming any attempts at actual fun.
Overall, Ordo Templi Orientis is likely to deliver nothing but confusion and frustration - it's a bad campaign that barely counts as playable.