If you swap Everquest or Ultima Online for Warcraft in your question, then you have your hits that the were genre creators, and the alternatives that arrived a

If you swap Everquest or Ultima Online for Warcraft in your question, then you have your hits that the were genre creators, and the alternatives that arrived a few years later (Warcraft, Eve Online, Club Penguin, Guild Wars, D&D Online, etc...) Or if you want to focus on Warcraft as the big hit that popularized the genre, then we can see that the secondary MMOs of today are over 10x size of the biggest MMO pre-Warcraft (Everquest peaked at around 600k subscriber, Elder Scrolls Online has over 8 million). No one game has been as big as WoW, but it did grow the overall market massively.