There is only two shots that really stick into the back of my head and I go “Now common…”
The first was in GB1 when the hell hound broke out of Tully's apartment, the camera cuts to a shot of the dog and it looks likes a puppet, it appears to show only the top half of the dog and it looks really akward to me.
The second is a little more humorous than “bad.” In GB2 when the bathtub lunges out for Dana and Oscar you can plainly tell that the slime is some guys hand under a wash cloth of some sort. Very clever of ILM, but it too just looked akward.
But where there is a few bads, there is a ton of goods. For the 80's, the animation of the streams looked really good in GB1 and ILM topped em with the CGI ones in GB2, the ghosts were excellent, still some of the best ghosts I've seen in movies, and the Scoleri brothers scene has got to be my favorite special effect scene. There you have it.