This may seem like a simple question on the surface, but there is actually a great deal of complexity to it. It boils down to what point you consider the game completed. Diablo 4 features a campaign story, but there is plenty to do besides just the main acts and seeing the final boss defeated. One of the biggest aspects that could affect this is the class you start off with. Not all the classes have the same damage output or the same survival rate.
In addition to that, you have to consider becoming as powerful as possible through end-game content. This guide will cover each milestone of this process.
Campaign: Around 30 Hours
A Gamespot interview with the game's director states Diablo 4 is a 35-hour experience. If you are just playing out the campaign on normal difficulty and enjoying the story without trying to do everything or skipping all the dialog, you are looking at around 30 hours of gameplay. This time frame can differ wildly due to many factors. It depends on if you explore every nook and cranny, and how often you backtrack completing a task. Changing the difficulty to a higher setting for better rewards and how many upgrades you have will also stack on some time. Consider this the first milestone in “completing” the game.
Skipping Everything: Around 15 hours
Thanks to some of the average reviewer playtimes collected by the good folks at GamingIntel. We can see that skipping all the dialog and rushing through the main story to get a character to the endgame content will see you spending about 15 hours doing so. If you have completed the game with a previous character, you can skip the campaign for other classes to save yourself 60 hours of grinding.
Endgame: 150+ Hours
Initially, you’re looking at over 150 hours of content if you plan on doing everything in the game, as stated by the associate game director for Diablo 4, Joseph Piepiora, over on his Twitter account. This includes getting your character to be as powerful as they can be. This number may climb higher throughout the game’s lifecycle.
Speedrunning: Unknown
Speedrunners will push to get better and better times in games. They will often discover and exploit every single trick they can unearth in this pursuit. For perspective, Diablo 3’s campaign is stated to be 18 hours in length. However, the speedrun record for the game is just over 1 hour and 19 minutes.