Is There An MMO You Wish You Played Before It Was Shut Down?

Over the course of the past two decades, many MMORPGs have come and gone. However, a few stick out as must plays for the genre, at least in the community. Unfortunately, not everyone has been able to play every major game to grace the annals of the MMORPG genre, especially those games that have shut down over the years. Is there an MMO you wish you played before it was shut down?