Nice reminiscing going on !
BG1 & 2
(btw just started siege of dragonspear few days ago)
I think the root of the problem is no studio has figured out the secret sauce to build a compelling hack and slash game : gameplay and replayability.
It tells us that even if you have the best technology/technical teams on the AAA genre in the world, the result will always be bland if you can't get it right.
D4 is obviously following the path of D3, a new upcoming failure and a new stain on the ruined diablo franchise.