well... possibly i'm gonna feel a bit alone in this thread, but here i go: what's wrong with possession?
3 out of 4 games in which possession is involved i'm being asked about banning it. but why indeed? i understand it is kind of painful to see "your" wonderful deck being used against you, as a sort of kidnapping or ripping. no doubt bearing that vulneration can be a hard lesson to learn, even though we're just playing a game. but beyond that primary reaction, there is a tactical richness to discover.
i can tell of a number of memorable games in which mindbending strategy suddenly popped up because of possession's unexpected effects: imagine herald, golem, tactician, goons, council room, ambassador, masquerade or black market combined with it; imagine games without multiple actions; i remember many games playing the poorer the better, crazy situations in which players compete to fastly weaken their own decks...
i've been amazed no few times because of possession, regardless of winning or losing my games. just give it a try, and have fun!