The thing about Diablo from the time it was brought out it spawned so many good memories and good games tried to spawn off this great classic it left everyone wanting more of this type or epic game play.
After Starcraft (which was excellent as well) Warcraft 2 and such many years of waiting Blizzard released Diablo 2 which was a drastic change and everyone was satisfied and then the expansion which was a great attachment to the original but I tend to agree with the system that with Diablo 1 had with not able to get past certain things without being a certain level and at least it was a guarantee that no one could skip content.
I mean it's obvious that they will take many aspects from World of Warcraft which will most likely result in more restrictions but that only results in much longer playability I mean it will always be Diablo because it's Blizzard who made it and it's blizzard who will continue to give us the greatness of these long play games with the 3d top view, the many spells, the great trading system, the combat system, battle.net and the community that loves and enjoys Diablo to the max.
And it seems to sell a game that continue to sells it's more player driven than you realize and when it comes out you will see that Blizzard will have created another great Diablo.