Having just re-played Fallout: New Vegas a couple of months ago, I've got to say that the idea of it being a lot better than Fallout 4 puzzles the hell out of me. Steam says I have over 700 hours into the game and I know it pretty well.
Mechanically speaking, Fallout 4 is vastly superior. I think we can all agree on that. The combat, the amount of content, the companions, enemy AI, the looting system--really, the improvements are significant.
There are areas where I give New Vegas the advantage. Random quests at unique locations, like the Vault with the plant life and the power plant/weapon complex. Fallout 4 needed more of those. I loved the way Fallout 4 told stories through terminals and letters but it needed more active quests no related to the main story.
New Vegas also lets you go evil almost immediately without needing to play the good guy for awhile first. I can understand why that's really hard to do with a much longer game, though. If they let you go evil right away in Fallout 4, you'd be missing most of the content.
The main quest-line, though? Uh, it's pretty much the same. Pick a faction. It's not much better or worse. After the revenge sequence is out of the way, the story falls apart. There is really nothing driving it at that point except that, apparently, nothing and no one can stop you from doing anything you want. The Legion, especially, is freaking stupid. I hated even looking at them because it took me right out of the game.
New Vegas is definitely not an example of a game with a strong main quest-line.
All things considered, there is no question in my mind that Fallout 4 is the better game. It's flawed, certainly, but so was everything else that came before, including New Vegas, which probably had more flaws.
