The Player versus Player (PvP) is equally good, and there are professions, crafting, and countless other things to do.
The missions are fun, the dungeons are rewarding (yet, accessible) and the raids are hardcore as ever. Every Expansion significantly improves the game and sometimes even dares to reinvent it. Legion was particularly great, especially for Mac gamers, as it moved the game from OpenGL to Metal, delivering a 61% performance improvement in the process. That success comes from the amazing support Blizzard continuously delivers.
The most successful MMO ever created, World of Warcraft (WoW) had at one point over 12 Million subscribers, more than all its competitors combined! To be fair, WoW’s subscribers may have decreased, but it’s still the most popular MMO out there, by far.