Vault 81 killed my early (positive) impression
 

All was going well till I found about vault 81 location from an adventurer who didn't "took an arrow to the knee" in Diamond City.
Another vault, stop the press I'm going there right away!

Is there anything that isn't broken on that location? Scripts are overlapping, NPC pathfinding is catastrophic, quests are broken (got lucky so none was left unfinished in the end), twin sister does not go your settlements although you persuade her to, molerats hang between floors, granny doesn't buy fertilizer although she said she would, teacher greets me "oh you must be the new visitor" although it's 27563585423th time I speak to her, etc etc.
It's like I'm seeing FO3/Skyrim all over again.

Is it just me or seems that Bethesda polished the early game to cloud audience's eyes, but more you uncover, more problems surface?

I completed the quest and had no issues that I can recall. Also loved the story behind it :)

That said, FO4 is just like Fallout 3 and Skyrim in terms of bugs to me. As in, it's surprisingly polished considering the scope and feature set - but it's full of little quirks and AI issues that occasionally pop up.

It's not as bad as New Vegas, thankfully - and unlike Obsidian, Bethesda can build a beautiful world that doesn't look like it's made out of cardboard.

I had a bug once on 81, but I reloaded and was fine the rest of the way. I didn't find a twin sister there, but I may not have done all the quests there yet. I restarted since then, so it may be a while till I get back that way.

If you don't follow the kid around vault, the whole questchain gets broken (just read it on FO4 wiki).
After you do the kid, you need to ask the hairdresser for rumors, it spawns the next point (the bloody cat).
Post cat another area opens with another sidekick wannabe and a bobblehead.
When you do even that, only then you receive twins (jet addiction) quest by talking to the twin sista'.

There is more. Among rumors was a girls' parents problem.
It's possible because my addiction quest got broken I can't ever receive that one. Broken in a way the twin sis never went to any of my settlements. The quest is considered finished in my journal.

The wiki also notes that after molerats the granny for whatever reason won't buy fertilizer any more.
Wiki does not list the addiction quest I'm talking about. Probably they got it impossible to do for some reason, broken script or something…
Add to that what I wrote, molerats hanging in the middle of the floor (maybe me activating the robot caused it?) and such stuff…
Hell Vault 81 is bug-o-rama in a small space. FO3/Skyrim clone.

Horrible area. Probably no betatesting in it.
I suggest making a separate save after each quest chain point and doing them carefully and differently if they bug out so you pull them all through somehow.

EDIT:
They've just added it!
http://fallout.wikia.com/wiki/Dependency
Seems that on PS4 it's even more broken than on PC, dunno how's that even possible LOL

About breaking the whole chain by failing to follow the kid is noted at the bottom here:
http://fallout.wikia.com/wiki/Hole_in_the_Wall
That leaves the unfortunate player without: