I genuinely wish that I had never played Champions Online. Not because I think it’s a terrible game or anything; far from it. While my experience trying to get the game to launch during beta was terrible, the actual finished game was really fun… but it was also pretty quickly broken and reduced to a shell of what it could have been. And that’s what makes me regret it, that it was a good game that will never deliver what it could have. A real “I Wish I Never Saw The Sunshine” moment.
Of course, there are people who wish that they had never booted up Mortal Online 2 or Phantasy Star Online 2, and I have at least one friend who wishes he had never played Final Fantasy XI because it directly led to him going down some self-destructive roads. And there are a lot of other games other there, a lot of games we might have given time but later regret doing so. So is there an MMO you actively regret playing?