Fortune teller is extremely strong if ever played before you force your opponent to draw a card. For instance village/Minion/Fortune teller is much stronger than a simple Minion hit. Odds that the opponent won't have a Minion in the 4 cards they draw go way up. Likewise, the card they get to draw from Council Room, Margrave, or Governor is much less if it will always be a green. Likewise, Fteller is very strong against other limited draw like Library or Watchtower if the opponent is using disappearing cash (e.g. Festival) - gumming up a slot really hurts their cycling and as a bonus if you are running limited draw, Fteller is cheap disappearing cash.
Some of the huge shots for Fteller are for attacks that target Green cards. The most obvious is Fteller/Sab. If they don't have estates then the combo assures they lose at least 2 VP if they aren't playing chips or complete megaturn and more often 3 or even 4. Fteller/Swindler destroys Alt-VP setups - turn Duchies into 5's, Fairgrounds into Golds, Gardens or Silk Roads into potions, it is not so hot against Feoda (too many free silvers) of course is terrible with Colonies. With Peddler out and no way to deplete the Peddler stack, Fteller/Swindler can destroy provinces with ease and most of the time Duchies as well. In addition a strong engine that can play the Fteller/Swindler combo 2 and 3 times on the last turn can destroy decent to huge points - particularly if you can gain the last province/colony during your action phase. Fteller/Knights goes strong against Alt-VP and can be strong against provinces with cost reduction (e.g. Princess). Fteller/Thief (or Pirate Ship) works well against Harems, but normally when that is viable the Harems aren't. All of these are double terminal shots and you really need a strong engine to hit them, they can let you claw back a win after you've started to lose, but they are slow and don't help you build much.
Fteller/Masq can work a bit - setup his next hand to have a big shiny green card in it and force him to hand over one of the other 4 hopefully high value cards (note this actively helps them other player in the early game). Fteller -> Tribute can be good if you want the Tribute to hit green; it is really strong if their only green are action/victory types like Nobles (this of course sucks if they have curses) or Harems. Late game, Fteller is great at killing Menage engines without discarding (you draw Prov/Prov/Menage/Menage/Nomad Camp and cry)
The big thing is not that Fteller is bad, it is that it is high variance. Sometimes it does nothing, sometimes it is a free Chancellor play. Reliably playing 4 card hands is annoying ... but most of the scenarios where you can hit that often are ones where you can also draw out of it.