Normally, I'd jump all over the chance to beat on Soulshift, as it tended to be a much-overcosted ability for what it did, but this is one of the few creatures that uses the keyword in a valuable way. Think of it like a restrictive double Raise Dead, which is pretty good. You can bring your Crypt Ghast and your Geist of Saint Traft to your hand at the same time, which can easily put you back on track to winning. The down side to that value is that you have to play a 4/4 for 5, which isn't that great for a creature. Also, a double Raise Dead might not be worth 5 mana to some people.
Pros: Double restrictive Raise Dead
Cons: Only on cheap Spirits, 4/4 for 5