D2 had new innovative mechanics that inscribed it’s name into the pages of legends.
D2 was further cemented and kept alive by modders. Legends such a Laz, whist and Harvest made great excellent mods keeping the game alive for years to come. Not to mention the further improvement by PluGy.
D4 doesn’t seem to have new innovative mechanics. Nor does it have mods.
In fact I’d say it’s a lot closer to Diablo 3, than it is to Diablo 2.
D2 takes time to learn, the difficulty spikes, uniques, making your own builds. Not to mention some of the crazy viable builds like a ZealSorc.
D3, is a lot easier. D4 is somewhere in between both.
One thing to note, is D4, is not for me. I’m not the target audience, so I’m obviously biased as well. D3 with it’s massive amount of paragon levels, is very much for me. I love D3 more than I love D2. Because for me it improved upon so many aspects of the gameplay, while it did take away some of the customization. The endgame was in my personal opinion better than D2.
I haven’t seen D4’s endgame. I probably won’t be seeing it either. So I cannot say if it’s closer to D2 or D3.
Story wise, D2 has more depth to it’s characters, the “quests” are more, streamlined and the cinematics are more dark. D3 is more, epic and grandiose. D4 seems to be more focused on the macabre and wants you to writhe as it shows you the story as to what I’ve seen so far.
Then there’s the end all be all of all the games. Combat.
Combat in D2 is, at best sluggish. and at worst, a skill shifting nightmare.
D3 is much more fluid, but somehow feels, less rewarding.
D4 sits somewhere in between. However, there’s a clear difference between Diablo 2 and 3, when comparing it to Diablo 4. Level scaling. If there’s going to be level scaling, then what’s the point of levels?
Diablo 4 is a medium between the complexity of Diablo 2 and the more casual friendly Diablo 3 experience.