In my opinion Diablo series does not cater any longer to the same crowd as Diablo 2 did which is why it earned the scorn of many - it's a Diablo for WoW fans and it seems to have been designed that way to the point that these both games actually are sharing design paradigms. PoE is the whole opposite of D3 in that its audience is that one which played Diablo 2 for competitive and - as has been said: for hardcore reasons. TL2 is really in the middle. People should be happy that there is a choice and no definitive best game. I backed PoE up to Gold level and also contributed at maximum level for upcoming Grim Dawn.
I personally - in retrospect anyway and despite me trying to play down its issues initially as well - do not count D3 as a milestone in gaming history in its current condition. Whatever technologies it promoted they didn't undo its game design pitfalls. For that matter technologies never really saved a game and using these as proof in the same way as sales shows that some people don't understand that games are not gadgets. You can't solely advertise used technologies in a game in order to promote its qualities!
Also in my opinion the game tried to cure too many evils at once but without adding many good gameplay-related things as compensation. They created a corset which they can hardly break out of so they are left thumping at their sales numbers (basically that D3 sold as much units as Assassin's Creed III) and botox'ing up their game until they fix it all in one expansion. Which would be within Blizzard's traditional canon anyway: Release the original game, fix the core issues which people were disappointed about in an expansion.