I've played Ragnarok Online private servers before, and really enjoyed them. However, the ones I played are either gone or with a really small/struggling community now.. not enough incentive to go back. I actually transitioned from the last RO server to Ragnarok Online 2 when that came out. The initial release was a lot of fun, but the first expansion ruined the game for me. I played for awhile after, but it was too buggy/p2w/grindy. I left for FFXIV, and would not go back.
I do really like FFXIV, though, so there isn't any compelling reason for me to revisit other MMOs or search for a new one to play.