9. Rainbow Six Siege
There are few more impressive examples of a game simply refusing to die off than Tom Clancy's Rainbow Six Siege.
For anyone who played the game upon launch, there wasn't much of an indication that it'd be anything more than an adequate tactical shooter which would be modestly successful for a few months before the player-base tapered off.
And indeed, Siege's launch sales were soft, attributed to the fact that the game was extremely low on content upon release, which in addition to a slow progression system and the inclusion of microtransactions suggested that Ubisoft were simply trying to nickle-and-dime players.
But Ubisoft stood by the game, and rather than quietly abandon it in the face of weak sales, continually released free DLC updates to bulk out the gaunt launch day package.
By adopting the now-popular Games-as-a-Service business model, powered by cosmetic in-game purchases, Siege was able to evolve into a consistent money-spinner for Ubisoft while offering up a content-rich AAA experience for players.
As of February 2020, barely four years after its release, Siege has amassed an impressive 55 million players.