Okay, one long meandering post ahead, and if reading this forum for the past 20 minutes has told me anything, it's that it will be immediately unpopular and I'll probably have half the forum demand I be banned for it, but what the hell. Oh, and there might be one or two spoilers, just in case anyone here has somehow not completed Fallout 3 yet. Fairly warned ye be.
Oh yeah, I also managed to misclick "Submit" instead of "Preview". I tend to build posts in strange orders, so I'm still tidying this up (it does read far too much like 'why I like this game' rather than 'why this is a good place to start Fallout').
The tl;dr version is "I really liked Fallout 3, and I think it's a great place to start as a Fallout fan."
The long version is as follows:
Fallout 3 happened to me entirely by accident. I was stood there in my local game store looking at the new released, picked up the game and thought "great, yet another Halo." Then I looked at the back and thought "Okay, someone was kind enough to nuke DC for the good of humanity. Starting to win me over here..."
Then I put it back on the shelf and walked away. About six months later, after a friend of mine explained what Fallout actually was, I figured the idea of a FPSRPG could be a fun idea, so I bought it.
I don't really remember what my first impressions were, but the moment I stepped out of Vault 101, I was won over. I bumbled my way around, got lost, ambushed and slaughtered in quick succession, and after quite a few false starts I eventually found my way in the game.
I'll skip the details, but suffice to say my first playthrough of Fallout 3 was an immensely satisfying experience. I remember volunteering to stop the Purifier overloading, standing there thinking "How the hell do I do this?" and then had the vivid flashback of my [character's] father reciting Revelation 21:6 - I am Alpha and Omega, the beginning and the end." The feeling of immense gratification at this personal revelation, and the subsequent Heroic Sacrifice, left me utterly contented.
Of course, it wasn't my only playthrough. In due course I grabbed every Trophy, beat every DLC pack and went batshit crazy a few times for a laugh. However, Fallout 3 stayed with me long after I put the controller down for the last time.
Because of Fallout 3, I gained an interest in the Fallout universe. I've spent far more time on the Fallout Wikia than is good for me. I even ran a Fallout-themed RPG for my local gaming group. I became an instant convert to the Fallout universe through this game.
Now for the record, I am not blind to the flaws of the game. Hell, I think it's a testament to how much I've come to love Fallout that I Platinum'd New Vegas before they released the major patches required to make the game playable. Fallout 3 is not a perfect game, nor is it entirely faithful to various elements of the previous games (not that I played any of them, but as I said I've read the wikias extensively and watched playthroughs of them), but I for one can live with that.
Maybe it is because I started with Fallout 3 and then learned the rest as I went, but I just cannot see why Fallout fans become so virulent towards it. For example, why exactly do the Brotherhood of Steel have to be the biggest arseholes in the country? From where I'm sitting, Fallout 3 justified the character shift pretty well; the Capital Wasteland BoS have officially split, and then split AGAIN into the BoS (who now behave as an organisation with "Paladins" arguably should), and to the Outcasts, who have stuck to their previous mission.
I've been trying to honesty look at my experiences with New Vegas and compare them, deciding whether I would have taken to Fallout as quickly or completely if I had discovered that game first. Obviously that's a very hard thing to do, but I suspect I wouldn't have. Fallout: New Vegas doesn't feel the same to me. Yes, it's clearly a Fallout game, but it's a Fallout game for people who already know what they're looking for. Fallout 3... okay, yes, it really DID oversimplify the living hell out of everything, but let's just ignore the opinion of someone who 100% cleared every other Fallout title a moment here; most people go by first impressions, and if you've got to hook someone fast, you won't do it by dumping stuff on them. You need bullet points; "Society = Gone. BoS = Good. Mutants = Bad. Enclaves = Stupidly Bad. Everyone Else = Bad if they shoot at you."
There is more to it than that, but the short version is that, on my intial playthrough, that is pretty much how I saw the factions. As I began to explore Fallout properly, both in game and beyond, I learned the more intricate and complex nature of the various political alliances, and began to spot what were likely nods to events I had no knowledge of, but others would. To me, T-51b was just a better suit of armour. By the time I bought New Vegas, T-51b was an iconic symbol of the Brotherhood of Steel as they had been in the previous games, and I even found myself thinking of the BoS in New Vegas as the "real" Brotherhood, and Lyon's men in DC as a distinct splinter faction rather than the 'equally valid' (or even ' the only') Brotherhood I'd thought of them as intiially.
So... yeah, that's the lot. I think despite it's flaws, which seemed to be far more noticable on my second / third go round, Fallout 3 did a pretty good job of conveying the universe to a new audience. Yes, it's very different to the older titles, but if Fallout 3 had just been "Fallout 1 / 2 with a graphics update", I doubt I'd even have given it a second glance. As much as I loved New Vegas, and as fun as I'm sure the old games are, I doubt any of them can quite match the 'wow' factor of stepping out into the Capital Wasteland for the first time...