I will say right now that bringing up stuff like "isometric vs first person" is nonsense. In fact, it's flat out stupid. The visual style of the originals was as much due to technical limitations of the time as anything; if Fallout 1 came out today it would almost certainly be first or third person the way 3 and NV are.
Not in fact so. NOT bringing "isometric vs. first person" leaves you without a big reason for everybody to respect each other, and when you get down to it - THAT is the only thing behind FO3 hatedom that couldn't, given enough effort be dealt with with a mod. Bringing it into the discussion also lets you see the problem with a hypotetical FO3 fanboy, and understanding why it's important can let you not be one and not have the moderator lock up the thread.
If you're not familiar with the other thread, it started out as outright flaming left and right and at some point actually evolved into a textwall heavy discussion, and then again devolved because everything got narrowed down to the core - the fallout 3 fan in that thread had the "1st/3d person = progress" mentality or "realtime is progress compared to turn based". This simply isn't true.
You don't have to obsess over the originals or even think too highly of them, but fact of the matter is, they were some of the very, very few turn based western RPG games ever made, ever since isometric graphics even showed up as the "future". Yes, at one point, Diablo 1 was revolutionary in terms of graphics, go figure. So was the first Fallout, chew on that for a minute - it even had a remarkably "streamlined" interface for an RPG, that only got to be a buzzword years after. And Fallout 2 was the big bloated sequel which messed up all the lore once upon a time. Fallout 2 was about as disrespectful to the franchise (and common sense, and everything, really), as was Fallout 3, even more so, when it comes to tone, lore, story and all that. But it didn't cause nearly as much outrage, and same people who couldn't take it as a serious Fallout game back then (including me) are still playing it today. Why is that?
Because at the time a turn based RPG wasn't retro, as much as revolutionary. There weren't any RPG games with graphics as good as Fallout which had turn based combat. And there never were any more until very recently. Another thing is that developing NPC's without the need for realistic 3d animation and voicework lets you create more of them - and more dialogue for them, for less money and with less staff. There's specific benefits to it, just as there are to full 3d all voicework approach. However, for ages Fallout franchise was the only one of it's kind - it managed to make the best (so far) out of isometric turn based RPG format.
And Fallout 3 just isn't that. Really, it isn't, that's neither a good thing or a bad thing. But you have to understand that the original Fallouts are very, very unique in the short history of gaming. They got plenty of flaws, and there's no real reason to overpraise them mindlessly, but when you come down to it - they have no competition within their genre. For about a decade, literaly, none at all, as in, everything else either wasn't turn based or wasn't an RPG. So whoever liked that sort of thing, and there's plenty of fans of that, grew to appreciate them even if they didn't like them or one of them initially. That's enough reason to be an originals fan - Fallout 3 can't really compete with what the originals ment or could mean to someone.
Why? Because Fallout 3 is a completely different game which belongs in a different niche, with a lot more competition and completely different values. For a lot of Fallout fans the cry "Why can't they make another game like Fallout 1/2?", for over 10 years, didn't mean "Why can't they make another game set in post apocalyptic america where you shoot stuff!", but simply "Why didn't anyone ever make another good turn based RPG?". So making Fallout 3 into anything BUT that either invalidates a lot of the reasons people loved the original ones for, OR really turns the franchise into something else. What did it get turned into?
An open world sand box 1st/3rd FPS with traces of RPG elements. Sure, I suppose there's people who think it's an awesome game and all, but I'd say it wasn't nearly as significant within that broad genre to warrant serious fanboyism.
So as an answer to the question - being a blind fanboy and fighting about lore and such is equally as silly and pointless, but I can find justifications for being a devoted fan of the originals, while I'm not too sure why anyone'd be a huge fan of Fallout 3 on anything but hugely subjective terms.
BUT! Simply looking at it as a clash between people who prefer different genres of games entirely lets everyone walk out of it without being an idiot.