Not very powerful in most situations. Very powerful in limited and specific conditions.
Didn't see this card first go around. It has some interesting counter plays but not sure if its worth a deck slot. Depends on the meta.
I think that only Highlander decks MIGHT be able to fit this in if they feel it necessary.
I think the best use is to use it with either Druid Quest or Shaman Quest.
Druid Quest AFTER you complete it. As the Druid, you give your opponent a useless hero power after you are done using it. Or if you don't have many choose one cards in your hand, use their active hero power for the turn and give them one they cannot use.
Shaman but not hero power activation. You swap hero powers for a turn, most likely they could not use it OR if they do get very little benefit from it.
Seems like an interesting card to play with, but best against certain classes with hero powers you want to deny or steal for a turn, like Boom hero power.
I do agree that a permanent swap at 2 mana is far too powerful or bad for the game. Now if this was a legendary minion at 10 mana, that would be different.