I find your list a little... strange. For instance:

BTTF3: it has a higher rating on rotten tomatoes, and there's no way you can call it a bad movie!

Alien3: the ONLY reason people didn't like the movie is because they killed Hicks, Newt and then, eventually, Ripley. It's much better than Ressurection or AVP.

Robocop III: Funny you put in T3, but left this out, this was a much worse movie - comparatively speaking - than T3.

Godfather Pt3: By no means as perfect a film as the first two, it is still a great film IMHO. It's not as if Mario Puzo didn't write it...

Rocky III: As sequals go, this one was decent, nowhere near as bad as Rocky V.

What about Saw III - probably the best of the 6 sequals :) Certainly better than the disappointment of Saw II anyway!