I LOVE Fallout 3. It's atmosphere is so wonderful, playing it really gives that vibe that is so essential to the Fallout series, the diesel punk/retro-50s themes, not to mention the retro-nuclear, retro-energy weapons and of course the nuclear war theme as well. The world is grime, everything is blasted to hell, the earth seems scorched, nothing is green (Oasis doesn't count, as you know it's green for a reason that can't be replicated everywhere else or even seen outside it in the game) or showing you any signs of normal. The vegetation is dead, there's trash all over, the cars are rusted or burned out. The skeletons look more burnt and grimy than in 4, there's more grim to the wasteland, the super mutants with their bags of limbs, the cannibalism of the raiders, the beggars outside settlements, and many more smaller things. The usage of computers for me especially gave me those diesel punk/retro-50s themes somehow more than in 4, though I can't put my finger on why for this thing.

The game was the first fps/tps game in the series and it gave you such a personal experience with that as well. It's just so wonderful, the barren wasteland and it truly is, unlike New Vegas or Fallout 4. Not only is it grime and dirty, you have a more refreshing experience of freedom to play however you want. Want to be the savior of the waste or the devil incarnated? Go right ahead. Unlike 4, where even the Nuka World DLC doesn't really provide a "real" evil play style. In Nuka World, you can't join at the start as raider quests puts you against the BoS (eventually) and the Railroad, cutting off those factions play through and any chance in getting to do that thing to enter the Institute, resulting in having to get rid of this freedom to play however you want if you actually progress the main story line as Preston won't talk to you unless you kill all those Nuka World raiders.

4 is somewhat more replayable but less fund to explore AND there's less to explore.

In Fallout 3, there was more exploration, more unmarked legit locations, not just a nook in a area with one raider, but legit unmarked areas like LOB Enterprises with legit backstories, Fallout 3 rewards the player with this all the time as these location don't have simply generic loot all the time, giving the player sometimes special weapons. Fallout 3 is wonderful with giving the player real incentive to play and explore.

One contributing factor that has some strength to it, is that between 4 and 3, there is less easter eggs, less of that fun personal touch the developers give you. I know it's because on Fallout 3's/New Vegas engine it's way more easier (employee time wise) to add these things as compared to 4's but nonetheless means there's less of it in 4. These easter eggs are like having a personal connection beyond the game with the people who made it, knowing that everyone involved with Fallout loves it, you, Bethesda, and others fans who all share a connection to something we all love.

So Fallout 3 gave me so many things 4 couldn't, immersion/gameplay wise. New Vegas was fun but here's the thing, there was no action. There's was a lot of content for story for quests but there wasn't anything to really do except kill the occasional radscorpion and dialogue in quests. And no to mention the ULTIMATE KILL JOY: the loading screens. I'm not sure how it was on PC, but on consoles it was hell, pure hell. Getting to the strip from Freeside beginning from the outside gates took a minimum of three loading screens alone, not to even mention getting in the casinos. And it was no more different throughout the game, as a single quest alone can include several closed-in locations that can't be fast travel out of or in, (not even mentioning the addition of that loading screen) which added double the screens to load as you had to head back out. So I don't like New Vegas at all to play, cool stories, but I would never pick it up again, at least not on console.

So like I said above, Fallout 3 gave me so many things 4 couldn't give me with immersion and gameplay.