how is diablo 2 not an rpg? what for you is an rpg?
Well, I can't really deny that it's an RPG, but it's the bare minimum of what I'd consider an RPG, which is why I generally ignore them in these questions. About as much of an RPG as Borderlands. Your actions impact little how the story unfolds leading to few opportunities to actually roleplay. Each sequel focuses more and more on the levelling and looting aspects which are somehow considered to be roleplaying. Which they indeed can be a part of, but not necessarily so. Dialogue exists only to give you the next mission where you're supposed to go an kill people or other random creatures.
Everything is solved by killing, there is no opportunity to pickpocket, lockpick, very little stealth in general. Diplomatic skills like intimidation, persuasion and such are also lacking. Path of Exile is the same. The emphasis on story, for example in Path of Exile is only slightly higher than the story in World of Warcraft. Not sure how it gets later, but I've gotten to level 25 in that game, and I found myself killing stuff constantly for random reasons I stopped caring about around level 17, because the excuses were pretty thinly disguised. Very similar to what happened in WoW.
It's the Action RPG genre in a nutshell. With a heavy emphasis on the action part. Still, they're generally accepted to be RPG's, hence the name, so I can't really be bothered to argue the point that they're not. However, what I'd consider to be the best RPG's are RPG's that allow for RPing something else than a killing machine while keeping the killing machine part fun.
To take Baldur's Gate as an example. You can play a smoothtalking rogue. Not a rogue that backstabs people, in fact, doing a smoothtalker would probably make you less effective in combat, so your character would actually strive to solve conflicts without combat, and when that is impossible, rely on the party to do the major part. This is not good in a minmaxing aspect, but the option is there.
Missions can be solved by fighting, talking, thieving, magic(detecting who lies), etc.