Terrible Card in Crossroads, Harem and/or Nobles game. More effective in other alt-VP games, e.g. Gardens, Silk Road. It is a double edged sword in that it can speed up your opponent's deck cycling so is bad in say Tactician, wharf, KC, goons, etc. etc. games. However, for flushing cards out of his deck and into his discard it is wonderful. To properly wield the sword you must A) correctly analyze the kingdom and B) basically be mindful of your opponent's deck as well because sometime it is best not to play the card while at other times it is the smartest play in the whole game (like when you know with near certainty his attack cards are upcoming and all his VP are discarded).
Personally, I enjoy playing Fortune Teller, If I'm reading CR correctly than I pick it up 40% of the time it is available.