There's a central loop in Diablo which is the underlying factor that makes the game's success or not working. Are you satisfied to Diablo IV Gold walk into the dungeon, mindlessly hunt down mobs and loot? If so it is, then Diablo 4 is halfway to being loved by its players. If the team has mismanaged the loot system in the same way as they did with the first launch of Diablo 3, then we're in trouble.
Within the novel Blood, Sweat, and Pixels The chapter that deals with the calamity that happened during Diablo 3's launch tells the tale of how a Blizzard designer played with the game for hundreds of hours until they came across a single famous loot. When that light in orange finally emerged from an opponent, he walked towards the loot and realized that his character couldn't even use it. The loot system was fundamentally flawed that the excitement that comes from grinding all day and then the satisfaction of getting something of value, was broken.
This was finally fixed to the point that you could only discover certain levels of loot that fit your class, and that the rate at which early-game legendary items were dropped was up. So even though the legendary items that you could get did not break the game however, you would occasionally get a small hit of dopamine to keep your hands on the rope.
If Diablo 4 gets that right and features a similar loot system to that of Loot2.0 that was in Diablo 3, then we're already concerned about how much time we're going to spend playing the game. The disaster in Diablo 3 is the best chance that has ever happened to the franchise on an ongoing basis, and combine it with an Immortal controversy, it's like Blizzard has a fairly simple list of potential potholes to avoid for it to stay at the top of the list of it's most loyal players.
The Diablo 3 community is very vocal about what it doesn't like and has been doing so throughout the lifecycle of Diablo 3, so we're hoping Blizzard is taking it into consideration from those fortunate enough to Diablo 4 Gold experience large portions of the game prior to release. But we'd also bet Blizzard isn't too thrilled with the flood of leaked footage that is rumored to have come on the heels of one of these private tests.