After playing Sunless Sea over the past week (mostly offline) I feel that I can rightly recommend this game. The content I've seen so far is very impressive, and I trust that it'll only get better.
First impressions, when venturing out into the unknown, there's a very real sense of anxiety. Early on, without knowing how far your fuel will take you, each time you leave dock feels like a one-way trip. However, each port has its own story to tell, and you'll always look forward to what you'll come across next. When presented with a fork in the road (RNG challenges), the risks are satisfying to make.
After a while (or after a death or two), you, as a player, become more experienced. You learn which ports to stop at when you're heading out far. You consider how much terror you can safely accumulate when you run without a lightsource. You'll get a feel for how much damage you can dish out and recieve. You'll establish a route or two that'll make you the most profit; what you should sell, where you should sell it, and what to keep for later. You develop a captain's mind. You have to, or you're dead.
Some peculiar observations, though:
Once I wrote a will, my outlook changed significally. I lost much of those early-game jitters, and likely won't feel them in any future playthrough since I'm already making lasting investments from this point on.
Also, once enough of the map has been explored, most of what's left to do is simply doing business. There's still more out there, and I'm still finding new things, but at this point, with exploration mostly out of the way, the game is starting to feel like a casual experience, sort of a darker version of Animal Crossing. Now it's mostly just earning more money and collecting stuff by doing repeatable jobs, while progressing maybe 1 or 2 story plots if it's along the way to my next payoff (could just be me; I did take the "get rich" ambition, after all).
Another thing that makes the game feel more casual is that the save system is fairly easy to abuse. By default, the game saves only when you dock. If you fail an RNG challenge, you can simply 'quit to title screen' and hit continue. If there's more business to be done that you know is safe to do, do that first, then hit the docking key "E" twice to leave and redock in an instant, updating the save so you can retry the challenge until it goes your way. It's unfortunate, but I'm all too guilty for save-scumming this way. Some of the best written content is only experienced once, and I really don't want to miss out on any of the stories and/or treasure.
I think the only technical thing I would like to see added to the game would be the ability to remap certain keys. I just want to be able to change the lamp-toggle to a key other than "L." It just seems to be the only command on the right-hand side of the keyboard, is all.