I agree with Bagstone in all the aforementioned points. D3 is a technically superior game and it should come to no surprise.
My problem with D3 (and most titles nowadays) is a general lack of RESPECT on a conceptual level. Meaning: The user to world approach is off, and that breaks the game (for me) on a fundamental level.
Let me explain, and please, try to imagine this from the point of view of a casual, not a fan that read all the novels before playing the game.
In D1 you were a nameless hero in search of fortune and fame. You knew nothing of that which you were facing, no monsters spoke to you (except Garbad and Lachdanan), your relationship to the world and its inhabitants was based on exploration and a very few scattered texts that where intentionally cryptically and obscure. You had to venture yourself into the unknown going deeper and deeper with the promise of power and the inevitable fight with the big D.
What is that monster? I don’t know.
What can it do? I don’t know.
What will jump out to eat me if I open that door? I don’t know.
Dying at the beginning of D1 was a very, VERY possible thing. And death meant, well.. That. Death.
The very first "boss" encounter with the butcher was intentionally designed to be unfair.. No cutscenes, no villain monologues (I’m looking at you Magda). You opened a door, and immediately started running for your life. IF you got to kill this fearsome demon, you were rewarded with a powerful item that carried you for a long time.
D2 continued the story of the nameless hero, added beautiful cutscenes, dialogues, etc. But the general INTENTION off all this info was to purposely mislead the player, building momentum for the big plot twist that culminated with LOD.
Then D3 came along and.. You are THE NEPHALEM. A creature so powerful that both angels and demons fear (literal words from Tyrael). There is no reason to fear anything, you da boss.
Diablo lord of.. Whatever BUT terror..
Whenever you accidentally step on a bug, a (magical?) explorer starts rambling about his own experiences with said creature. Decard Cain opened up a bag shop and left free bag samples all around Sanctuary for you to find useless lore? (then got killed)
Everything in D3 is desperate to show some form of personality and connect with the player, even if that means ruining the atmosphere.
Azmodan sending you invoice messages every 5 steps? Even Legion himself cannot fight the urge to give you the lip whenever you do something.. Weren’t these guys planning this for like.. eternity? How can the player be in complete control of the situation, but just five minutes late?
Diablo the lord of terror is afraid of you.
Imperius, the embodiment of valor, is afraid of you.
Azmodan, the greatest commander of the burning hells isn’t wreaking havoc on the battlefield, leading the charge.. No, he waits for YOU on an arena type throne room, as if he had nothing better to do than to just wait for you to kill him.
I could go on and on..
The point is that the focus of the first 2 games was on the monsters, history and atmosphere, whereas the third installment caters to the egocentric point of view of the current "player base".
Not really sorry for rant, cheers
Ps: I still play every season on D3, solo self found. Season 6? It took me 2 days to be facerolling T10 with my monk.. Just finished installing D2 again.