I did a Turducken once. It wasn't "bad", but I wasn't all that impressed with it. There was just way too much going on with it. While the flavors meshed well, I think they really masked eachother in the process, though.
And seeing as how the total cost was a pretty penny more than a 4 bone prime rib roast (and more than double the cost of a 4 bone choice rib roast)...yeah, not worth it.