I think the craziest turnaround story was Final Fantasy XIV, which was so bad at release that the following shitstorms meant that everyone expected it would go the way most MMOs go (soon forgotten). But not with Square-Enix (who had a money maker with their previous MMO Final Fantasy 11) who commited to revamping the whole game which took basically 3 years but in the end it became a really good game with a lot of happy players. (I have not played it myself so would like to listen to what players themselves say!)