Sure, MW had a very coherent world but the gameplay was painful: awful combat and non-existing quest design. Fargoth's Gold was hand-scripted to impress the journalists but even this quest was fairly simple: follow the guy at night, which unlocks his hiding place you can't find otherwise. So once the magic of the visuals wears of, there isn't much left.
Fallout 3 had a pretty good quest design, which made the game more bearable for me. From the review:
"Side quest design is one of the strongest and most enjoyable aspects of the game. You have choices, consequences, multiple, often very different solutions, skill- and stat-checks, effective speech options, NPC reactions, etc. This design is very good (suffering only from poor writing) and I can only hope that it will be used extensively in future Bethesda titles.
...
One of the first Megaton quests is Blood Ties. It starts as a generic “deliver a letter” quest but quickly grows into something more complex. You discover that the family the letter was addressed to has been murdered (a successful Medicine check reveals the cause of their death) and their child is missing. Local residents inform you that a local gang may be responsible. You are given 3 possible locations where the gang could be found. No hand-holding. So, now the “deliver a letter” quest turns into a “save a kid” quest. Once you find the gang, you are free to attack them and save the kid. Or you can talk to them. Entering through the gate unmolested requires a bribe, or the above mentioned letter (it’s possible to initiate the quest without having the letter), or high speech, or a certain perk. When you talk to the leader, it transpires that it was the kid who killed his parents (which is a nice and unexpected twist) and the gang is helping him to control his urges. At this point, what you do is up to you. You can leave the kid with the gang or take him back (if you think this would be wise). You can still kill the gang ending the settlement’s problems with them, or you can broker a deal (protection for supplies)."
Basically, MW had a better world, lore, writing, but combat and quests - which is 90% of what you do in an open world game - very subpar. Fallout 3 was the other way around, so it depends on your tolerance level. If you can tolerate bad combat to enjoy the lore, MW is a better game. If you can tolerate the amusement park setting of Fallout 3, then FO3 is a better game.