This is a personal, largely spoiler free (or spoiler-vague) review of the The Outsider fan-made campaign by Carl Stephens (CapitalBathory) for Arkham Horror the Card Game.
Taking place immediately after the Lovecraft story of the same name, The Outsider is a 3-scenario long campaign that involves the investigators chasing after a strange monster that intruded in on a party, following it underground to the strange world where it came from.
The Outsider is one of the very earliest fan-made campaigns: the first scenario was out before the Dunwich Legacy was even finished! This ends up showing in interesting and awkward ways, making the campaign more of a historical note than an actual fun campaign to play. While only three scenarios long, the end of the campaign hints at more that was never made, leaving the whole thing feeling like an early, unfinished prototype.
The story presentation of The Outsider is thin - there's not even a campaign long, and the first two scenarios have no reading beyond the Act and Agenda. It's not until the final, third scenario that there's any additional reading - in the form of a single paragraph on a set-up card. There's not much of a story, with it rolling off of the beginning of the original short story - after the strange, lonely creature in The Outsider intruded in the party and ran home, the first two scenarios involve following it - first over the church grounds, and then into a ghoul filled underground castle. The third scenario then involves an avatar of Nyarlathotep and finding The Outsider, rescuing it, and teaming up with it. Taking a story about loneliness, depression, and isolation, and then adding in "And then you become friends!" is certainly a choice - but it's funny and brazen enough choice that it's hard not to respect it. It's a shame whatever the next step of the story was was never finished.
As for the play of the campaign, it ends up being extremely simple - there's not really any twists or unique mechanics in the first two scenarios. You progress forward, gathering clues, and just move ahead without anything really changing that plan. The second scenario does require you to get a key with an Intellect test and use it with a Willpower test, but even then it's only a single test of each, which seems gentle compared to many other early fanmade campaigns that often require ridiculous tests. It's not until the third scenario that actual gameplay from the campaign is introduced - an extremely wild, complicated map full of one-way passages, and a Hunter enemy that when he catches up, deals you damage and moves you to the furthest location (luckily, there's a card to let you know where that is, because the map is SO wild!). It's a neat premise, but feels a bit undertuned - the locations themselves aren't interesting enough to change gameplay any, and the encounter deck does little to contribute. There's little in the way of actual flavor in the mechanics, making the entire campaign feel like a half-baked tutorial.
Overall, the campaign isn't particularly good - it's luckily not painful to play, like some can be, but it really just Arkham at it's most barebones. If you're interested in it for a historical look at what people were playing for fan made campaigns early, take a look - but if you're looking for something fun or new to play, it's an easy skip.