I'm going to do at least two more playthroughs of FO4, because my first was as part of the BoS. I worry I might have taken the best route first as I hear the Institute and the Railroad are both very lacklustre when compared, But I am still going to try them out.
After that it'll just be free-roaming and playing with mods because sadly there isn't all that much replay value. I'm not sure what Bethesda was attempting by making the character able to work for all the factions at the same time until the very last moment, but I think they might have been genuinely scared that people would get angry that choosing sides could potentially mean some parts of the game would then be unavailable to them. People are so used to having their cake and eating it too that being "punished" for making a choice is an alien concept to them.
I can fully imagine someone in this day and age saying "I chose to side with the institute so now I can't do the BoS final missions? Worst game ever". As a result almost nothing you do has any consequence and that really takes a toll on the longevity of the game. Now that said, I have never finished the civil war questline in Skyrim, and only finished the main quest once (and I barely remember it at all) because exploring the world was just more interesting than the main quest. Despite this I've sunk over 400 hours into the game.
I think at least 150 of those hours have been spent on mod content like Moonpath to Elswyr and other great quest mods, and with Enderal coming out in English in a few weeks that'll be 400 more hours with what looks like the biggest total conversion ever. Will the same happen with Fallout 4? I doubt it, with everything from the voiced protagonist making it impossible to have conversations with new NPCs, the complete lack of new animations and generally weird scripting, I don't see many questing mods or overhauls being made for FO4, and Bethesda is already pulling out with the last DLC in a couple of weeks too. It almost feels like they're preparing to take the cash and run.
Also looming in the horizon is when they'll introduce paid "premium mods" for console owners. Which no doubt will be a sight to behold. Personally I hold out faith that they'll lend the license to another company like they did with New Vegas and we get a Fallout with all the good things from FO4 and less of the bad. One can hope anyway.