The difference between the backstories in other Fallout games and the one in this game is simple. The other games gave you a backstory that was beyond your control to choose or completely inconsequential. We don't choose our parents. A job as a courier doesn't establish you as one type of person or another. It's just a job and there's limitless options to headcanon that backstory.
We DO choose our spouses and whether or not we engage in activities to produce children.
The character creation tool, while clever, made me cringe because I couldn't identify with either character. I'm not a military man, nor a lawyer woman. I'm actually a military woman; a cross between the two. However, I can't really roleplay that and gosh it seems completely weird that this former lawyer is now running around with a minigun, a sniper rifle, and power armor. I mean, who the heck IS this woman? She's definitely not my character.
With games previous to this, your slate was pretty clean. The extent of life choices made for you for the sake of story were minimal and things that were either inconsequential (courier) or beyond your control (father). This? This game never lets you forget that you are happily heterosixually married and searching for the fruit of that union. You can never even rewrite it in your headcanon because somehow every single npc in the game, whether you've talked to them about it or not, knows about it and beats you over the head with it. You can't even play as a character who isn't talking about his or her backstory because for certain quests, the only 'correct' option is the one that says "I am out here looking for my baby! Where is my baby! I'm nothing without my baby!!!" You can't even have a romance with an npc without having to revisit this deceased husband (that I'm pretty certain I never talked to that particular companion about) and tell them "I can love you both!" Good grief. Really? If I could have at least kept my headcanon that this was a marriage of convenience... Nope. I loved him, apparently. My grief is so profound that even a character I'm trying to initiate a romance with feels the need to inform me of how in love with this dead guy I *seem*.
It's just not immersive for anyone who wouldn't have made these life choices or would have made them in a different way. It forces people into a very defined box and that was the one aspect of the Fallout and Elder Scrolls franchises that set them apart from all the other games that have a fixed, often male, protagonist. It's why I play these games instead of games like The Witcher. Played, at any rate.
Now, I'm ok with the idea of searching for a baby. I just don't think they needed to go this route to write that story. The kid could have been your nephew or sibling and been just as compelling a scene to watch. I'd care about going to find that baby, because again, that's something that would have been beyond my control and doesn't require me to suspend disbelief. I can't control whether my brother\sister has a kid, nor my parents. I can only control whether or not I have a kid, but that's apparently not a choice Todd Howard thinks we should have.
Eventually, I just accepted that this is Todd Howard's character and I moved on, but gosh if it doesn't sour me on the entire franchise. It's really made it so I don't even want to play the main storyline or try out the other romance options. I don't even know if I want to play another Fallout game and I am praying to any and all gods listening that they don't let him NEAR another Elder Scrolls game with these ideas. Bethesda games as we knew them are no longer. Now they are just like every other game.