Is it possible to make a non-isometric game in Diablo franchise? Sure it is.
Will it be perceived by users as a complete Diablo game? Probably not. It’ll be viewed as a spin-off of the main lineup, and they better not give it a number as to not to offend some sensitive souls.
The thing is, a serialized game like Diablo makes people expect certain tropes and certain FORM from the next part. They don’t simply want a new game in the same universe - they want the next part of the series. And that means that there should be certain elements that make it similar to the previous parts.
For example, imagine the next Uncharted game take out puzzles completely and become open-world non-linear adventure. The fans of the series who respect Uncharted for the plot and linear adventure and platforming will be disappointed. Because they basically didn’t get a game they hoped for.
Look at Resident Evil 7. It is actually a good game for people who like horror games. But because it has almost NOTHING to do with the actual RE series, it wasn’t very well received. Many fans of the series simply didn’t buy it. It changed everything completely - from genre to form to the acutal main plot direction. It’s not about zombie apocalypse and Unbrella corporation - it’s about surviving in a house with a bunch of mad maniacs. I don’t know enough to tell if it IS actually tied to RE universe at all, but I do know that even if it has some connection - it’s too shallow to actually be considered a part of RE series.
It is, for all intents and purposes, a spin-off. And should have been called something like “Resident Evil: Alone in the dark” or whatever. But because it’s a main series, many people felt put off by the fact alone.
When you make the next installment of a SERIES - you have to make sure that the lements that your playerbase loves and expects are preserved. Not only the base genre - but also certain tropes and FORM of the game.
As for Fallout - in all honesty, I don’t think that the new 3rd-person games have anything to do with the originals. They are different games. It’s basically Post-Apoc TES at this point.
Also, let Bethesda burn in Hell - I’m not buying any of their games after what they did to 76, and thank god I waited for reviews. Unless they fire Todd with shame and make an actual, real good game that the reviewers will sing praises to. I don’t care of what they show in their announcements from now on one bit. Endless piles of Indie crap is more trustworthy at this point.
One final thing I want to note is that people HATE differences. Look at D3-D2 holywar. Objectively, D3 is a good game, far richer in features and content than D2.
Certain people hate it solely because it’s not the same as D2. It doesn’t matter if the change is objectively good or bad - any difference is automatically perceived as a negative.
And then they go and invent far-fetched justifications for their hate. going as far as to say that farming fixed-difficulty Baal that posed no challenge to well-geared characters and that promised exactly the same route and enemies each run - was way more fun than clearing randomized greater rifts that are always appropriately difficult for your character, highly diverse in content and give you a goal and psychological reward when you clear one GR higher than before.
People will say all sorts of nonsense to prove their belief, even and especially when their belief is baseless.
TLDR: Making spin-off games for popular franchises is OK. Change the main protagonist, the genre, the form - keep only the setting consistent. And you can make a good game.
But if you are making the next part of the series - Diablo 5, Starcraft 3, Warcraft 4, Call of Duty 137 - they better be close enough to the original in both genre and form. Because that’s what people want from a sequel.
If Blizzard made non-isometric Diablo 5 that in all other respects and gameplay was very faithful to Diablo franchise - many people will be put off simply by the wrong form. Simply because their expectation wasn’t fulfilled.