I've been playing Fallen London for at least 5 years now, with a few different characters. I never wanted to review it before because I was worried it would be transitory, and that once the company went under no one would ever be able to play the game I had written about.
But it has been doing better than ever, and has in the last few years added a ton of new content which has significantly improved it.
In form, it is similar to old facebook text games like Mafia, where you have a bunch of numbers for resources and items that change around as you click. The difference is that this has really nice backgrounds, a ton of well-written text (I think a couple million words?) and a card-based system for storylets.
The game is set in a version of London that was sold to dark Masters by queen Victoria. It was taken underground, where the laws of physics no longer apply and death isn't permanent. Hell is a neighbor, and fungus and candles replace plants and sunlight.
It really is two games in one: the first is a time-gated system of customizable stories, with sixty or so actions spread throughout a day (or 80 if you pay a monthly fee). These stories include sweeping epics of revenge or battle against extradimensional beings that changes entire countries or the world, as well as smaller stories like fighting a spider in the sewers.
The other game is a carefully-balanced resources game. Each 'click' has an optimum number of resources available, growing larger until the endgame, and some powerful items take months to save up for. Some hardcore players compete to buy extravagant items like a hellworm or a cask of immortality-inducing cider.
Many storylets are re-used; so, you can bust a 'tomb colonist' (kind of a decayed sentient zombie) out of prison over and over again. Some are only done once, like deciding whether to support a local mob boss or his cop daughter. The re-used ones tend to occur in 'grinds' which are pretty common in this game, although much less than they once were in the early game.
To me, the best stories are:
-Making Your Name, early storylines that help you progress the four stats: Watchful (used for detective work with a Sherlock Holmes substitute, archaeology or university work studying bizarre magical languages), Persuasive (used for romantic and creative work, including writing operas and engaging in courtly romances), Dangerous (used for fighting duels and capturing monsters), and Shadowy (used for pickpocketing and elaborate heists)
-Ambitions. These are stories that span the entire length of the game, starting from something simple (usually tracking down an old friend or lead) and ending up dealing with godlike beings. They include a horror story, a revenge story, an adventure story and a sort of legend or fantasy about wish fulfillment.
-The final stat-capping storylines. These include the railway, an end-game segment where you become a railroad baron, building a railway to hell that gets stranger and stranger the further from London you get; the University Lab, where you discover the dark secrets of the Masters; a series of wars that you lead as a general in a bizarre place; and elaborate thefts that make you a legendary thief.
The game can be 'completed' without paying, but the monthly fee makes grinding a lot easier and provides access to some amazingly good short stories called 'exceptional stories'. Older exceptional stories are available for a fairly hefty sum, but they are generally worth it (especially ones by Chandler Groover and Emily Short).
There's a lot of interesting material up front in the 'making your name' segments, so it's worth checking it out just to see the overall style and feel.
Edit: Looking at the other reviews, I'd say their criticisms are absolutely true (stories can be shallow, clues and hints are items instead of actual stories). I just can't give 4 stars after having played this game for hundreds of hours and honestly investing over $100 or $200 in bits or pieces after years.