Swisher has a career .805 OPS as opposed to Kotsay's .751 (though the highest OPS he's posted since 2005 is .746). I would expect an improvement from Swisher's 2008, since his career high LD% produced a very fluky H%. However, Swisher is pretty bad everywhere in the field except 1B, where he's decent. Kotsay sucks in the field too, though.
The Yankees gave up Wilson Betemit, Jeff Marquez and Jhonny Nunez for Swisher and Kanekoa Texeira. Not exactly a king's ransom. I would definitely prefer Swish.