Combined with nitro boosts, goblin glider and burning rush it really gave you the fun kind of mobility in combat and out of combat. No game has really allowed that kind of fun mobility it feels like, aside from Sekiro and Quake games.
Then there's mentioning the playstyle which was fun. The new summoner demonology while thematically very fitting is just so boring to play and feels weird. Affliction without dot snapshotting is just hollow, and they try to make AOE spells work for it every expansion but nothing feels right. Destruction without havoc and shadowburn by default doesn't feel right, since it was the only part that required "skill".