Ok... I completely finished the game last week.
I don't want to post any big spoilers, for those of you still in the middle of it. But I've got to say -- the game really builds in intensity near the end. The story line gets GOOD and sucks you in, making you want to put in a LOT of time playing to find out what happens next. That's the good news. The bad news? Absolutely weak ending "cut scene". It leaves WAY too many questions unanswered. In fact, it's SO bad, it left me confused for a little while -- trying to keep playing a bit to find another mission that would advance the story further. I had that sinking suspicion of, "That may have actually been where they ended the main story ... but it CAN'T be! Let me wander around a bit and keep talking to people to see if they do anything else here." They didn't.
As I look the game up and read the discussions about it that include the spoilers, I see where this was the consensus of almost everyone who played it all the way through. Bethesda released additional DLC called "Far Harbor" last month that's supposed to add a lot of new content on the map and new missions. But right now, I feel so bitter about the ending, it makes me totally unwilling to pay a dime for more content that doesn't even address where they dropped the ball on the main story!
Supposedly, some people have picked through the source code for Fallout 4 and found a lot of evidence of pieces of the story they originally intended to put in, but skipped over. I have a feeling this game was a victim of sales/marketing people and others internally who demanded it ship by a certain date, at the expense of developing the ending further.
If people on here have also finished and want to talk more about it, I'm up for that! But for now, let me just say that you wind up under a lot of pressure to make choices which force you to side with one group over the others. In many cases, you're going to conclude (as I did) that the optimal solution is to try to get more than one of the groups to work together - but the game won't give you that opportunity. You wind up choosing a side, reluctantly, because of the "hope" or "gamble" that before the end of the game, you'll be able to leverage that decision to make some changes and turn things around for everyone. But they're not going to let you go there. This *could* be addressed in a Fallout 5 game if it was designed to continue where this left off -- but they didn't even make this feel like that was the plan. (No "To Be Continued" popping up after the cut-scene or anything like that.)
Hmm, I'll add my two cents when I get there!