Definitely an interesting card. I was running it in my previous olympian list. It scales well - it can be counted on to do 6 damage by 5 mana. So it works like Lightning Strike. That makes it undoubtedly a great card.

On the other hand, the only deck faster than War is HRD, and retribution is a dead card in that matchup. That's why Sam is using savage strikes. Against control, retribution is useless against sleep and order. It can clear frontliners, but this deck routinely gets creatures so big that it runs them over.

So in summary, the biggest threats are cats with knives, order, and sleep. Retribution doesn't help with any of them.