Well, I guess it hugely depends where one's coming from. Hence my question which RPGs you played before. (There's a reason why I didn't mention Fallout 2 btw, I don't think it stands out from the crowd particularly well.)
We obviously rate the game differently. Please don't get me wrong, I don't want to diminish your appreciation for Fallout 3. If the game captured you so much, then I'm happy for you that you found something that you enjoyed so much. But let me try to explain where some of the differences might be.
First, you praise the game a lot for its content, and played only 200 hours. I just checked; I played 83 hours before the boredom overwhelmed me. Compared to other games of its type, that's pretty much a failure. Fallout 3 is the first Bethesda game that I spent less than 100 hours on. I sunk a couple hundred hours in Oblivion (after mods turned the initially broken design into something enjoyable), and definitely more than 1000 into Morrowind. Had I played Fallout 3 for 200 hours I'd still say its mediocre compared to other games of its type.
Then, you mention freedom of exploration. I don't know, I can see how it may look like this for a player used to more linear gameplay. For example, if someone came from FPS games to Fallout 3 (not saying that you did, just an example), then I can see how the world of Fallout 3 looks vast and open. However, when I played Fallout 3, the first thing I noticed when I entered the wasteland was how small the map is. I went from the Vault to Megaton, looked at the distance I already covered on the main map, and thought "Please don't tell me that that's the only map of the game." In Morrowind, I spent several hundred hours before I had even explored a quarter of the map. Then, Fallout has lots of buildings that you just can't enter. A player coming from an FPS background probably wouldn't even think about that as a limitation, but if you come from vast RPG worlds where every building has an interior, can be entered and explored, and is occupied by people with whom you can talk, then Fallout's "lots of space" begin to feel pretty fake. Speaking of people to talk to: Why are Fallout 3's NPCs so limited in their dialogue? Why can't I ask them about their beliefs, about the area they live in, what they think of other factions, or what they think of the people they live with? Ever since dialogue has gone "fully voiced", the amount of dialogue in games has been cut down tremendously. Planescape (IIRC) had 800.000 characters of dialogue, try to find that in Fallout. Then, where's the detailed background? When I played Morrowind, the third town I entered had a bookstore. And I spent two hours of real time reading through the books there, immersing myself in the strange and original stories of alien gods, or Dunmer folklore, or the first glimpse of the lost and forgotten Dwemer culture. Where does Fallout 3 have something that comes even close? Before that, in the second city I entered, I probably spent half an hour asking a priest about her gods and her beliefs - 9 gods, each one with his own domain, and that's just one of the belief systems you can encounter in this world.
Then there's the main quest. In Morrowind, you uncovered millennia-old mysteries in a conflict of mortals turned into god-like beings. None of the characters is black or white, each one has his own motivations, each one has his own explanation of the past events. You work your way to at least three totally different, contradicting accounts of what actually happened, you always wonder who might be telling the truth or who might only be manipulating you. Similarly, Planescape:Torment puts you into a rich universe as a mysterious character who cannot die, who lost his memories, who has instructions tattooed on his back, and who desperately tries to find out who he is. You meet people who may have met one of your former selves, and again you can never be sure whom to trust. No character has "friend" or "foe" written on his forehead, angels might turn out to be mad, and the evil witch that everyone fears might help you more than anybody else - or she might not, who knows if you can trust her. Now compare that to Fallout 3: the main quest is about securing a water supply for the people of the wasteland, and (presumably) preventing it from falling it into the hands of the Enclave. From the first moment, it's clear that securing the water supply is the "good" thing to do. Your father is a cardboard cliché "good" character if there ever was one, and while I hope that the Enclave may be more than a bunch of misled militaristic autocrats, I kind of fear that they are just the "evil" counterparts to your father's "good" intentions. It is utterly boring. It doesn't give my mind anything to do. Everything is laid out clear before me as if I'm just following instructions. Do you want to be the good guy, follow plan A. Do you want to be the bad guy, follow plan B. Yay for choices. Yawn.
I could go on, but I don't want to bore you as much as Fallout 3 bored me in the end. As I said, I totally understand that Fallout 3 might be positively overwhelming to someone who has little experience with former RPGs. But put beside those, I can only see it as a step backwards. It has its moments, but it doesn't really capture me.
"post-apocalyptical Washington DC" just leaves less room for variety than a setting like "strange fantasy subcontinent with several thousand years of history buried underneath" does, and it shows after a while ... at least it did for me.
