Walking into a Deadend Hallway that had a Mega Goblin Spawn as a Multishot Demon Hunter on T13. Murdering 20+ goblins at once and it just raining Legendaries.
The best part of Diablo 3 is the Set dungeons, or rather trying to master them for the first time. There are many guides that make them trivial, but doing them the first time, by trial and error, felt like a real challenge, almost like Challenge Modes in WoW used to be, but solo. I wish for more content like this, where gear matter very little, or rather stats as some specific gear were needed, point is, Ancients etc barely made any difference, which is awesome. More "scaled" content please!!
• Diablo Immortal is the most misunderstood and underrated game of all time!
• Blizzard, please, give us some end-game focused Classic servers, where you start at max level!
• Serious Completionist: 100% OW Achievements, 100% D3 Achievements, 90% Immortal Achievements, 99% ATT Classic, ~90% ATT Retail
Probably a bit dull, but defeating Diablo for the first time on Inferno difficulty.
My character wasn't quite ready for it yet (I believe it was on a WD with all sorts of inconsistent random gear equipped) and I took quite a few attempts. Finally killing him was very satisfying at the time.