Campaign Recommendations
This list is a grouping of the fan made campaigns I most recommend playing, grouped into tiers by what I see as their quality. It doesn't contain every campaign - only the ones I've played - and each link to the full spoiler-light review for that campaign. Within the tiers, I have them listed alphabetically - not in any sort of priority order.
Strongest Recommendations
These campaigns are all ones I find excellent - I think you can pick these up and have a good time from start to finish. While some are more complex and difficult than others, none of them have any real failure points.
Alice in Wonderland by The Beard is a solid, approachable campaign that does well to balance scenario uniqueness and thematic throughline. In it, investigators find a collapsing Alice at the Arkham train station, and have to journey to Wonderland to keep the shadows consuming it from taking over the real world. It might be on the easy side for my experienced players, but it's got a good sense of whimsical writing and clever mechanics.
Ages Unwound by Olivia Juliet is a fantastic campaign that smartly plays with the idea of time travel as the investigators fight against a cult trying to unmake time and reality. It has a tight, singular focus, and stands out as one of the greatest fanmade campaigns.
Bloodborne - City of the Unseen by aughhh is much like the videogame it seeks to intimidate - challenging and rewarded, and filled with lore. It's difficult, complex, and long scenarios aren't for everyone, but for those looking for a challenging, it stands out in the field.
Call of the Plaguebearer by Dr. Jack Science is a great campaign for Arkham veterans that draws heavily from Resident Evil and The Reanimator. Its repeated use of Arkham locations builds a happy familiarity, and its mechanics, while complex at times, provide a wide variety of fun challenges.
Circus Ex Mortis by The Beard is a Shub Niggurath based campaign with an extra of circus theming. It's spooky and tense, with a fantastic design and comes with a great circus themed investigator card expansion, too.
The Colour Out of Oz by The Beard is a strong campaign that requires your full focus - as the investigators quest through Oz fighting against the corrupting influence of the colour, they'll meet a wide variety of characters. The multi-goal scenarios and treachery cards with upkeep provide cosntantly shifting board states that demand full attention.
Cyclopean Foundations by The Beard is a Cthulhu based campaign that's as close as you can get to feeling official from a fan-made campaign. It's focus on specific mechanics gives it a strong mechanical theme.
Jumanji by The Beard is only four scenarios long - which means it's got no cruft to it. Based on the 1995 movie,t he campaign cleverly incorporates the mechanics of the game in a short, tight experience.
Medium Recommendations
These campaigns are all good, and I think you'll have a good time with them. Each of them, however, has some flaw keeping them from greatness - be they mechanics that don't feel good, or some scenarios that are more frustrating than fun.
Darkham Horror by Frostgrave closely follows the plot of the videogame Darkest Dungeon, it's got all the challenge and bleakness of the videogame. It doesn't have much in the way of complexity, though, except for its over-reliance of encounter cards that can stick about. The back half of the campaign flags, however, and the player card expansion it comes with isn't well designed.
The Ghosts of Onigawa by Myriad is a good campaign with lots of rough edges. Set in Japan, half of its scenarios are brilliant and down to earth horror, and half miss the mark trying to go for a more epic feel, with the end of the campaign being more of a miss than a hit. Still, whats good there is quite good, and makes it worth checking out. The player card expansion that comes with it is also fun of lots of fun ideas.
The Matter of Britain by Frying Tonight is a pulp adventure focused on the legend of King Arthur, and is an extremely ambitious campaign with tons of story paths. Still, some of its scenarios falter - while most are brilliant - so it can be a rougher experience.
The War of the Worlds by The Beard is a three scenario campaign based on the novel and radio drama. It doesn't try to do anything too fancy or ambitious, but it also doesn't really have any low points - it's a short, solid campaign you can playthrough in a weekend.
Weak Recommendations
These campaigns are by no means bad - and often have some great scenarios - but lack of the consistency in design strength of those on previous lists. They're fun, but expect things like rules mistakes or unrealized potential.
Celtic Rising by Qggonew is a five scenario campaign set in Ireland. It's scenarios are mostly good (with the last one falling apart), but its attempts at introducing a new stat just falls short. Its story text is thin, however, and leaves the campaign feeling like a group of disconnceted side scenarios.
The Crown of Egil by anaylzechris is a four scenario campaign set in Iceland, centered around worshippers of a mythological poet, trickster, and berserker. It has a lot of interesting mechanical ideas, but fails to pay a lot of them off at the end, leaving it disappointing. While the story is barebones, the mythological tales woven throughout make up for it. It's a good time, but feels like it could be just a bit tigther.