I do think the OT has some pretty wooden dialogue. Just looking over JennyS1138's list of great dialogue, it really is all in the delivery! It's memorable but is something like "Governor Tarkin, I should have known it was you holding Vader's leash. I smelled your foul stench when I was brought on board" really a great line? It's pretty stilted and I know I wouldn't be caught dead saying it. It's just memorable because Alec, Harrison, Yoda and the gang made you believe in the words with the way they said them. That's something that's in short supply with the actors in the prequels.