I've completed Far Harbor. It's pretty decent overall. I mentioned earlier that it has new creatures, new equipment, and a cool new setting, but those aren't the only ways that it improves on the base game. The bullshit radiant quests are gone, replaced with a number of sidequests that were properly scripted out. Even the story, despite my previous misgivings, isn't all that bad. You have to deal with three factions that are at each other's throats, like the base game, but unlike the base game, you actually have options on how to resolve the situation peacefully, and aren't forced to take part in a genocide if you don't want to. Is there more bad cribbing from Blade Runner, of course, but at least this time you aren't given a prescriptive role in the story, and thank God, there's no weepy family melodrama forcing itself front and center this time. Seriously, I know I've complained about that last point a lot, but it deserves stressing. Bethesda is the last dev in the world that should be trying to tell these personal, emotional stories about love and family. You can't half-ass a story like that. To do it well, you really need to go all in and focus on that element. For a dev like Bethesda, which doesn't even bother hiring professional writers to do their writing, the idea of prioritizing good writing like that is a joke.
One thing that I will criticize, although it's a minor point, is how companions are handled. You're expected to bring Nick along, because part of his backstory is revealed on the island, and so there's a lot of dialogue with him to that end and all that, but he's the only one. None of the other companions - except for one guy whom you meet there, but he doesn't really add much to anything - have any situational dialogue or anything to contribute to what's going on. I suppose it would be pretty difficult to make it so every companion has their own little subplot there, but picking and choosing one doesn't feel right to me. I prefer what NV did in offering you new companions in its add-ons.