Diablo 3 becomes anything from weak to terrible, after just a couple hours of play. Of course, this does not mean you can return the product.
Without the Diablo 3 brand, this game would have received a 50-60/100 score, modest sales, and flown under the radar as just another big budget but generic title.
The product cannot simply "be fixed". The two most important, fundamental areas where the team went completely backwards are:
1. They decreased depth, rather than building upon what works and going deeper.
Diablo 2 was a massive success because it embraced what people loved about Diablo 1, then provided a new layer of depth and breadth to the experience. Depth is a difficult concept to describe, and it is particularly important in gameplay.
To give one example: an additional difficulty where all mechanics still function the exact same does not bring much additional "depth" (if any). Particularly, if this means completely stupifying the two lowest difficulties, which then simply become formalities the player must sit through in order to reach an actual challenge and build the character.
How about Blocking actually being an action this time around for some classes? Parrying?
How about the location actually having an effect on gameplay (heat, cold, weather)? Perhaps tailoring some equipment to the environment, rather than walking through a molten hot area that looks cool but has Zero impact on gameplay?
How about the need to rest? People actually Enjoyed having a reason to go to town in Diablo 2, believe it or not.
How about the passage of time, rather than the feeling like an entire run through the games story takes place within like 3 hours?
I cannot believe we have all the hassle of being always online, but you still go into a town and it's empty.
What works on one enemy, works on all. They look so unique and well animated, but it has almost zero effect on gameplay. Again, the issue is lack of Depth.
And now you might understand some examples of "Depth", I could go on for hours with more.
2. A completely backwards perspective on the previous product (Diablo 2) and how its mechanics fit (or not) into the new vision.
Relentlessly during the Diablo 3 development, nearly every aspect of Diablo 2 was put-down, including publicly and in marketing material, in order to build hype for the new utopian mechanics that would be so, so much better. This approach, particularly when putting down the fundamentals behind one of the best selling products of all time, should have raised red flags from the very start.