Not OP, but if you mean Diablo IV specifically:

Pros:

-Returns to its more dark and gritty roots.

-The franchise as a whole has fantastic lore/good story. Like good enough to where if nothing else check out some lore videos here.

-If you like diving into buildcrafting it is a pretty good series to get into. Same goes for if you like grinding for better loot.

-The different classes are all pretty unique and all classes offer multiple ways to play the class. For example on Druid tou can be a Werewolf that zips around clawing at enemies at highspeed inflicting enemies you melee with a bunch of poison. Or you can be a Werebear that slams the ground to cause earthquakes to cast out in front of you. Or you can focus on throwing out tons of tornadoes and lightning. To name a few.

-The game is going to be supported for quite some time, as i believe are two planned DLCs for the game plus regular seasonal content. In fact they are almost to season 30 of Diablo III and still supporting that game.

-The devs have become very committed recently about being open on the when and why of any changes well in advance.

Cons:

-The game is still trying to find itself balance wise. In xp drops, in class skill balance, in armor abilities, in resistance stats. Key features that were added later in Diablo III’s lifetime just straight up not brought into IV for some reason.

-This is oversimplifying it a lot, but the above plus some previous lack of open communication of changes has lost a lot of goodwill between players and devs. To the point they had to have a kind of emergency meeting stream about what they did and make promises to fix. So far it seems they are doing what they can to keep those at least.

-The monetization is fully in your face. Now i will say, IMO it is not the worst game by any means. There arent any pay to win mechanics from what i have seen (a big problem in Diablo:Immortal), but the cosmetic stuff is there, it is advertised, and IMO pretty damn overpriced.

-The endgame right now sucks. Now I’ll preface this by saying this should be one of the promised things changing very soon. But it currently really only consists of running harder and harder versions of the same dungeons with limited lives over and over and over again. And the way the dungeons are made harder is not just the enemy level, but with modifiers that a lot of players feel to be unfair. Like having enemies crowd control you in place repeatedly preventing you from moving or acting as they just simply kill you.

That said, all in all i do recommend trying the game if RPGs/ARPGs even remotely interest you. Id give it something like a 7.5/10, and they do seem pretty committed to the long haul of supporting and improving the game. You could easily sink 30+ hours into the game. If you would like any more detail on any of those points id be happy to answer.