EverQuest: A trend setting multiplayer game and critically acclaimed "best in the MMORPG genre". EverQuest set the industry standard for online gaming. It was one of the first 3D games in the Massively Multiplayer Online genre.
On that note, I would like to point out that in total, EverQuest has had 19 expansion packs released so far since their 1999 release. The latest expansion, "Rain of Fear".
After 13 years, EverQuest adopted a Free to Play model. And after 14 years it is still going strong.