I haven't even actually really finished my first playthrough yet, because I'm so frustrating by the way I've boxed myself into a corner as a quadruple agent. The only faction I don't feel like I'm actually deceiving is the Minutemen, which is probably part of the reason I'm so enthusiastic about them.
I keep restarting my playthroughs trying to find a build I like, only to get a little fatigued with micromanaging settlements, resource collecting and replaying the same bits of story over and over.
I really should just remember to focus on the main quest and that everything else is optional. 
To be honest though, I think the major sticking point against it is that I just feel less invested in FO4 than I was in FNV. While I like Bethesda's work, it does seem to me that Obsidian often do far better at presenting the consequences of our actions in game, how morally grey the choices could be, as well as really allow us the freedom to really get involved with and engage in cross-factional dynamics from time to time.
Still, at least in FO4 we can actually romance the companions, rather than forced to endure shipteases that go nowhere like in FNV. And since Cait is basically Cass, I can't help but give FO4 bonus points for finally letting me romance her... or at least her Irish Doppleganger.