The editors over at All Purpose Blogger have editorialized about what they'd like to see in a hypothetical-yet-inevitable Fallout 4, which includes some of what made Skyrim and New Vegas more memorable experiences in certain areas than Fallout 3. A sampling:
The Skyrim Treatment: A lot of people loved Skyrim. The size of the world, the quality of the graphics, the entertainment of the gameplay, all of these aspects were awesome. And throughout my time playing Skyrim, I was constantly thinking (imagine how awesome Fallout would be if it saw the same treatment). Think about it. The jump between Fallout 3 and New Vegas wasn't massive, but it's a step forward. But the jump between Oblivion and Skyrim was huge. So why can't Fallout get the same sort of makeover? If they get similar gameplay, graphics and scale into a game in the Fallout universe, the possibilities are almost endless.
The New Vegas Treatment: A lot of people may think I'm mad saying this, but hear me out first. I enjoyed New Vegas more than Fallout 3 not only because it stuck closer to the original fluff, but because you appeared to have some sort of choice in your story arc. Granted, a lot of missions for the NCR or Caesar's Legion (or even Mr House for that matter) may have been the same, but you still got to make the decision of who won the war in the Mojave. Now take all that choice, all of those alternate endings, all of the extra areas and side quests, and tie it up with the scale of Skyrim's main story, side quests and map size and you're looking at a game of epic proportions. A true sandbox game with a storyline worthy of an RPG: the prospect is epic, right? Throw in more of the same with companions and their quests and, in my opinion, you're on the track for RPG perfection.