For me, Vader's silence was much more complex. You didn't know what was really going on in his head... you knew he was part machine, and you knew that the "good" in him was being denied by some dark forces. With his silence, you really wondered what complex stuff was going on in there -- if his old neurons were waking up and fighting with his new neurons, or exactly what. The "nooo!" destroys all the complexity that his silence allowed for.

Although in a sense, I suppose the "nooo!" makes him seem more like creepy Anakin from the episodes 2 and 3, the whiny one who always wants his way. Maybe that's why some of the gushers like it.