I'm guessing your referring to the Executor crashing into the Death Star. I suppose the biggest reason I don't like it is that the shot lingers too long. While the other two films used similiar tricks with models (and in a probably even more amateurish fashion), but with good camerawork and editing, they were able to pull them off. In this particular shot, the scale seems wrong and they both look like models, at least moreso than any other shot I can think of. And don't get me started on the "out of control barbeque" flame that comes out of the Death Star that the camera seems to stay on way too long. I think some faster cuts or a different angle might have worked better.