Diablo 1&2 had unimaginative stat systems that had mathematically perfect solutions for each build, usually generic.
Diablo 2 had a ridiculous skill system that essentially only worked for a rushed/powerleveled character that hoarded points, and spent them on a minmaxed build later on.
Diablo 1&2 had a hostility system that encouraged griefing and uncooperative play with people other than friends. This was compounded by having all loot drops able to be snatched up by the closest/fastest player. Duels were generally held in the same spot for most games, with no balance and the safety of town to run to.
The only thing that could possibly be defended as good is the art style, and from the screenshots and video's, it's not far from the originals, with plenty of gore and violence.