I liked playing Diablo III because so much of it is like Diablo II. And Diablo II is amazing - especially if you got the Lord of Destruction expansion, which added a whole fifth act and two character classes. In fact, one of those classes is the Assassin, and she’s the coolest, so we should probably consider Lord of Destruction as the definitive way to play.
Diablo II has aged well, for the most part, as isometric RPGs often do (see also: Arcanum; Fallout). There's something very comforting about the pattern of a ground made from the same square tile of grass or mud repeated ad infinitum. Like the carpets at school. It’s the game that my big brother taught me to click-to-move on. I was approx. 10 and things you play around that age stick with you. Mainly I love it for the sound. The weird glug noise that potions make, the papery unfurling of a scroll, the ting! when a gem dropped. Also, the zombie noise is very, very funny.
Diablo II has all your favourites: living skellingtons!; snuffling gremlin things!; your favourite magic book boi Deckard Cain!; hurling traps and grenades behind you at the big demon monster and running around in circles to maintain distance!; cinematics that are now so bad they're hilarious (pictured)!; runes!