All of the series are classified as graphical dungeon crawlers: The first Diablo is clearly closer to original roguelikes, despite being real-time. Diablo2 is more about statistical min-maxing of character builds. Diablo3 is just about finding the best items for equipment.
But IRL they're skinner boxes with behavior shaping "RPG elements" that are incredibly addictive. They all use the danger of death and statistical manipulation to force item-grinding and gold-collection to get better equipment - it becomes a competition on min-maxing equipment as opposed to skill builds and D3 is especially bad with this "skill balancing" throwing out most of build variability of D2 skill selection(that only game in the series that has a moderate variety in skill choice. D3 Builds are incredibly reductionist cookie cutter damage builds.RoS expansion fixed some of it, but it clearly a shadow of D2 builds.RoS generally feels more like D2.) and adding paragon levels to add unlimited grind potential. Its simply more like a single-player MMORPG adapted to local needs.