Interesting that I disliked F3 and I am curious how F4 qualifies as soulless? Not a fight, interested in your perspective.
Fallout 3 is probably my all-time favourite game world. I'm not sure exactly what makes it so immersive or gives it such a sense of place, but after playing Fallout 4 I don't think Bethesda know what it was either.
In terms of the story, starting with a child rather than a fully formed adult was important, because you can imprint your own identity on him right from the beginning. I cared what happened to Vault 101 because I grew up there, and the story about lies being told to keep everyone afraid to venture outside was better than Fallout 4's baby-snatching nonsense. When you first open the vault door and step into the sunlight - that's a classic gaming moment, far better than anything Fallout 4 had to offer.
Having Fallout 4's character become a soldier for the Brotherhood or a Minutemen do-gooder seemed out of place to me. Why would he do that when, as far as he's concerned, it was only a few days ago that his wife was shot in the face and his infant son kidnapped while he watched.
Fallout 3's character is a wanderer in a new world, willingly exploring, becoming whatever you want him to be. It makes more sense, regardless of whether you decide to help people, kill people, fight mutants, get rich...
Fallout 3 is more open-ended, whereas 4 relies on a large number of characters who, because the story is so linear, are indispensable. If you kill somebody in Fallout 3 you must face the consequences (or reload) but Fallout 4 doesn't even give you that option.
Fallout 3 is dangerous - the first time I wandered into a town that had a Deathclaw was genuinely scary. I didn't last long and I didn't go back until much later. Strap on some Power Armour, which is more common than shotgun shells in Fallout 4, and you're basically invincible.
The Tranquility Lane mission - nothing in Fallout 4 is as memorable, imaginative or surprising, but Fallout 3 has several of this quality. The Oasis area, for example - who saw that coming? In contrast, very little in Fallout 4 is particularly original and even the 'follow Liberty Prime and do something with a reactor' ending that I had is very similar to 3.
So, there you go. Not that I didn't like Fallout 4 to begin with - I thought it was going to be the game of the year at first - but as it went on my enthusiasm turned into disappointment.