Logged a couple hours into Far Harbor last night (couldn't get it to load night one) and am beyond impressed with it.
First off... the land mass is pretty damn big. Based on what I'm seeing I'd say there is at least 25-30 hrs of content here. Likely more for a player such as myself that likes to explore every angle and gets carried away building up settlements.
The setting is very atmospheric. In a lot of regards the narrative is quite different than what we've seen in the Commonwealth. The fog is almost a character in and of itself in Far Harbor and the inhabitants all seem to have a story that's a part of a bigger mystery. It's all very immersive and mysterious feeling like an expansion of some of the best aspects of the side quests, namely Nick Valentine's quest (one of my personal favorites.)
A few things I did before embarking on this quest given you're leaving the Commonwealth that I'd recommend others do as well...
- make sure you take your most valued companion as you won't be able to switch up once you've sailed away.
- take a good variety of weapons with you. Even though there are a few new powerful weapons exclusive to Far Harbor you'll only have access to what you take with you and the inhabitants of this island are pretty formidable.
- take some bulk materials so you can build up your settlements quickly rather than relying on the resources around you. I haven't secured any settlements yet but think this plan will serve me well once I do.
Like I said I'm not too far into this DLC yet but it's pretty freakin' awesome. In a lot of ways I like the more focused (not to be mistaken with linear) objectives as opposed to very loose Commonwealth environment. Anyone that enjoys this game should invest in this DLC. Even at full price it's worth it. Just my 2 cents.