Story additions is the single player are competent, but not the focus.
The addition of Rifts, random 4 player dungeons, at different tiers of difficulty did alot to revamp this game, and make it both more social and more fun.
With 2.1, the additions of Greater Rifts, which increase in difficulty, allow a great way to compare yourself to thousands of other players around the world. Also, treasure goblin realms, seasons, and overall QoL improvements have made this the game that we all should have had 2 years ago.
Basically, if you like loot hoarding dungeon crawlers, it's hard to beat D3 in it's current iteration. It plays fantastic, and is addictively fun to play with others, whether they are strangers or friends.
The continued support and additions forcast a long and positive relationship with this game for years to come.