I am fairly familiar with Flatland, but only had a brief glance at Fallen London prior to this game. Flattened London is a truly delightful mash-up of the two. Featuring a consistent, weird, and lovingly created world that shines of respect for its inspirational material, it offers some of the most intriguing exploration. In this world, most everything is strange, but naturally so. It also remains mostly unexplained, but also naturally so.
Both the writing and the puzzles are impeccable, and fit right in, both in the narrative and in the world. Descriptions are just as detailed as they should be, and almost everything has been implemented thoughtfully. Although puzzles are slightly on the easy side, they are fun, and there are enough of them to delight and amuse; most of them can be worked on in parallel. It also seemed pretty clear that there are several ways to solve several of the puzzles, and there are several possible endings. In the end, I managed to reach a particularly enjoyable one in just over two hours. All through this I only stumbled on a few minor issues with the implementation, which is greatly impressive for a game of this size.