Diablo 3 was never a difficult game and from what I've read, is massively less 'difficult' than it was at release. Because they set the game up with an overly simplistic system that revolves around a primary stat, vitality and resistances, that was the only hurdle to either being one shot or living. I dropped the game after a little over a month from its release. It was a simple matter of getting my vitality, resistances and main stat high enough to finish Inferno then you realize the game is garbage and has nothing Diablo 2 did to keep you interested and you quit.
The problem with Diablo 3 is that there is zero depth, complexity, commitment to your character, interesting itemization, pvp of any significance/fun and social system that encourages playing with everyone else. Basically a host of missing items that Diablo 2 had.
They didn't make an arpg, they made an action game. I liken Diablo 3 to Call of Duty in a medieval setting. There is no skill system, just a loadout, just like CoD. Your skill is a weapon choice and the rune is the weapon attachment. It's absolutely pathetic. Path of Exile, Diablo 2 and similar games are an example of what makes a proper skill and customization system in an ARPG. Diablo 3 is not an ARPG, it's an action game designed for consoles and released first on PC.
What kept Diablo 2 interesting and games like Path of Exile compelling was the depth to itemization, the huge myriad of possibilities you could find for unique builds and customization via items. Diablo 3 has a brain-dead system where you stack your main stat, resistances, some vitality and then get some crit modifiers and one of two life regain stats. It's done on purpose because they are catering to the lowest common denominator so the entire game is easily mastered and you just stack stats and watch your numbers go up. You see this highlighted when you read garbage from Blizzard like 'people just went to websites' Yeah, the people you made Diablo 3 for did 'just go to websites' They designed the game for your typical watered-down WoW player to pick up and understand in 2 minutes.
This is just one epic fail in the game. This is not even touching on the horrible social dynamic, lack of enjoyable pvp, micro-transaction infestation, complete lack of area/map randomization and the list just goes on. Never mind that the other major compelling nature of Diablo 2 was the item hunt. When every item in Diablo 3 boils down to main stat, vitality, crit and attack speed, it's hard to excited or interested in hunting for items that are that bland. There are no game-changers, no cool and unique rares that rolled with really unique modifiers, no single item that opens up a whole new build for you, no breakpoints and the list goes on. Just stat sticks of primary stat, resistances and the other three needed stats. It's WoW with RNG applied...
There is 95% wrong with the game and 5% right, and what is right is about two things; the combat/game engine its self and the art design is well done, albeit not exactly in line with the feel of the real past Diablo games.