It is a good game, a great effort by the team working on it, but such a shame that they did not care enough to really think it through and make it a masterpiece it had all the potential to become.
I don't want to go through all cons and pros, i'll just state the main issue:
THERE IS NO END GAME
Yes. And in games like Diablo, end game mechanics account for 95% of success. Everybody wants to get faster through leveling, right? In order to farm endgame activities. Now, there are two problems with the end game in D4:
1. Nothing to do. They brag about 150 dungeons or something. Now, almost all of these dungeons look so alike that it's unbelievable that it passed their QA and everybody said it's an AAA game design. Dungeons are horribly designed, a lot of dead ends, a lot of running around looking for stuff. Remember the action packed D3? Forget it, this is a running simulator.
In reality there are about 20 dungeons that can be Nightmare Dungeons, which present pretty much the only endgame content. And you just keep running the same dungeons over and over again, bringing the stones to pedestals, chasing the last monster in the area, etc.
Oh, right, there are helltides. Well. Same thing over and over and over again. Just run around the area aimlessly, killing every pack that you find, dodging fireballs and killing the most useless boss in the history of gaming.
2. The first issue could have been forgiven if there wasn't another problem: there's no reason to do all that. By level 70-75 your build would be pretty much complete. Yeah, you can find boots with +1% stats after another 100 hours, but you won't get any significant upgrades. There are no chase items. Oh well, there are extremely rare uniques, but as far as i know in billions upon billions of gamehours, only a handful of people found them. Think of the extremely complex and satisfying end game in PoE? Forget it. Here you will be running the same dungeons, filling out your inventory with useless items just to sell them hoping for any kind of an upgrade for you gear. And yes, you will need to pick up and sell everything if you still need to hit that crit chance on your ring after 50+ rerolls.
To sum up, D4 is like a business-class Mercedes with an interior of 1986 Toyota Corolla. It looks good, it feels good, it sounds good, but it is so plain and empty. It could have been such a great game. And it might be a great game in some time. But they really need to address the end game, and all the QoL items such as stash space, gems, outfits, respec, etc etc etc.
As it stands now, it's just another case of a large corporation selling the same brand again and gain. 1000% marketing, 10% caring about the player's experience.