Diablo 2, take your laptop to an uninhabited island, plug it into solar charger and knock yourself out. Continue it for years.
Diablo 3, no internet, no game. Ever.
What else is there to compare. Nothing. You can't play one of them to check.
I agree with the sentiment, that the online only is a deal-breaker.
Still even ignoring that, Diablo 3 was the WOW or Disney version of Diablo. It's not simply about graphics but also tone, atmosphere. In games that have that you can't simply take it away without loosing something important, even critical in some instances.
Diablo 3 may have some modern improvements but I'd much rather play Diablo 1 (with Belzebub) or Diablo 2 (with PlugY/multires). They hold up surprisingly well, played through both earlier this year and enjoyed it, at least until in Diablo 2 when getting creatures basically immune to both/all my magic damage types pretty much forcing me to rage quit.
If I wanted something modern and online only I'd go play Path of Exile again, something which Diablo 3 can barely hold a candle to. Also while having played a bunch of ARPGs recently, old and new and even re-releases (such as TQ Anniversary) the crafting/gear from PoE has me disappointed with them all in that regard. I can still handle simple skill systems but the stupid crafting just annoys me constantly. (Crate also needs to wake up already when it comes to stash storage, for heavens sake).
At this point I have no excitement about a new Diablo, expectations are not positive and my requirements seem to conflict with that Blizzard is/does these days. I almost hope whatever it is they add more superficial online requirements so I can just spare myself any optimism and time and just skip it.