For me, it's the post, post apocalyptic stuff that they dropped the ball with in this one that felt like a true waste of potential. Compare the logos to the other fallout games, fallout 1's logo is broken and falling apart, fallout 2's logo looks like the first one but with a jury rigged 2, it's glowing and it has wires sticking out of it, implying that the world is attempting to rebuild, Fallout 3 takes it back to the look of decay and ruin, which fit the environment, the New Vegas logo is a lit up sign that isn't pre-war but was made by people of the new world show how far we've come, then Fallout 4.... a completely perfect platinum logo, with hardly a scratch on it.
http://i.imgur.com/FauGraF.png
Even the early screenshots and trailers showed a world that looked like it was getting truly rebuilt.
http://www.recoilweb.com/wp-content/uploads/2015/06/Fallout-4-3.jpg Look at the buildings, they look like they're actually being repaired properly, something we see in New Vegas even. What did we get instead? Well we got absolutely no explanation as to why the buildings look like that. Everything is just overrun by mutants and raiders like it's Washington DC and there are only 2 "cities" I'm aware of in the game...