I have no opinion of this since I didn't bother to play 3 but grew up on 1 & 2 as well but I think we NMA community are getting exactly what we deserve with Fallout 4/76 and future Beth projects too. I hope Beth put Fallout 76 and make a Fallout 69 for mobile one day
I'm not sure if you are joking or not here (Oh the internet), lets say you don't. I would say the Fallout community (of the original Fallout games, and I hate to do the separation game, but I have to) is by far the most critical community out there with one major difference to others: You get good reasons and good explanation as to why somebody doesn't like something, without the plain and simple "this is shit" outrage with "and it's like" and "you know like" fillers in between.
People tested Fallout 3 and gave it a shot here, and so did I, and while it says Fallout: You can't bullshit people when it comes to gameplay and the more intangible aspects of the franchise (look and feel etc.) and you'll always get a good explanation as to why as I have mentioned before.
With Diablo 3 we talk about a whole different beast here. When D3 dropped, D2 was out for already 12 years, with many people 1 year in playing D2 classic before Lord of Destruction came out. The game went through many tweaks over the time span from 2000 to 2012, this is a pretty long time for an ARPG, naturally you loose a lot of players but also gain new ones, and you have old players return sometimes.
When D3 came out, while D2 was still playable you had Baal Bots all over the place and empty servers making it difficult to fully access all the advantages of the game and also complete certain quests. You basically had a handful of very loyal D1 and D2 players waiting for the release of D3, who still had the right age (time time time) to even get into the game in the first place, which was very different from the situation with Fallout, with an also very loyal fanbase which waited (felt like centuries) for a new installment of the game forever, a basically dead franchise was revitalized.
With D3 many players from WOW came over to play D3 (D3 incorporated a lot of the crap from blizzard Irving team into the game). You had a seemingless new release with a huge name behind them (Blizzard) to attract new players in a split second.
Totally different challenges, different backgrounds.