Fallout 1 - when you waste your limited time trying to enter the wrong vault without a chip simply to die inside and ruin your playthrough, I felt like saying "OMG this is the [censored]tiest and most overrated game I've played in my life". Then you start a second character giving no [censored]s about anything or anyone, and you find out you can kill a bunch of ghouls to get one chip. Up to this day I have no clue if you can get the chip in any other way but I always feel bad about it.
Fallout 2 - when you start the game and no matter what kind of character you create you are forced to finish that dungeon and beat that guy, it's the most OMG why the hell did they program this crap to be so annoying and absurd. I dropped the game there because it made no sense to me and it didn't even fit the fallout theme. I had a second OMG moment when I figured out you could run.
Fallout 3 - When you create a character that looks kinda old, and you are forced into a story where you are a 19 years old boy, I have a OMG who the [censored] thought it was a good idea to force the age of the protagonist and give you such an specific role. And a second OMG moment when I first got to shikenhab or whatever it's called, I had some sort of a sniper char first, but I shortly after a few quests I found that weapon and forced myself to go for a melee one, turns out I was having so much fun I decided to get bad karma just to get more chances to kill people. A third OMG moment when you first enter DC.
Fallout New Vegas - When I step outside doc mitchell house as a melee character due to the fun I had with my fallout 3 one, then I got north, east, north east, or any of those places, and I get an OMG why the [censored] they turn the game into a linear experience. I was forced to go south if I wanted to kill [censored], and follow a linear progression. And an OMG how boring after seeing the atmosphere, a [censored] desert with barely anything of value, I had to mod the game to remove the brown filter because it was uncomfortable to look at. And a last OMG moment when I learned you could disguise as an enemy faction, something I always wanted in bethesda games but they never implemented.
Fallout 4 - I saw the perk list before playing the game but since I went in the dark I didn't know what each thing did, I had an OMG moment when I realized they don't let you see the perks until after you chose your attributes. I had to check the pipboy almost immediatly after getting it or I could miss it. I had another OMG moment when I got the power armor but not becuase it was awesome, but because I couldn't realize how to get out, I was running out of the core, and I was sure what I pressed to get out, I didnt want to use a PA in the game anymore. It was the same with a lot of other mechanics the game does not explain to you clearly how to do things or what they are for, or what has changes from older games, the game treats you like if you already know everything. My name was on codsworth's list, and the Danse's quest.