Sunless Sea is a cornerstone of narrative-heavy games. Sunless Skies, the sequel, is better in many ways.
But not in all. I bounced hard off this game for a couple of reasons.
First, the controls require more practice. You have a slippery little flying locomotive that can strafe and aiming is hard.
A bigger issue that almost killed the game for me was the pacing. Sunless Sea had islands grouped in sets of 4-6, with the more dangerous and interesting islands found to the south and east. You could sail east and see everything dangerous, die, and restart, but it was all technically accessible early on. The 'safe islands' near the home port were more safe and boring.
In Sunless Skies, the map is way bigger (with 4 huge worlds), but your entire first world is like that 'safe' region. Ports are gentle and nice, and everything is slow paced. I almost lost interest.
But the other worlds are far better for my tastes. London is full of politics. You can join the rich in their fantasy lands that are gilded cages or you can work to rally workers to rebel against their masters. You can betray Victoria or nurture her child.
Eleutheria is full of darkness and poetry. It riffs on one of the most popular Exceptional Stories of Fallen London (Hojotoho) and has the same vibrant and dangerous feel that Saviour's Rocks or the Chelonate had in Sunless Sea.
The Blue Kingdom is small, but its ports have tons of options, and its 'small ports' are bigger than many of the real ports in the other worlds.
The story content here is immense, with more choices that you can take. Descending in a bathysphere through a black hole was amazing, and confronting Victoria with the true contents of the Serene Mausoleum was also excellent.
Highly recommended. I've played more than 60 hours and have quite a bit left to go on my current storyline, and I plan on doing a different storyline afterwards.