My list (best to worst):
1. Three-way tie:
Star Wars (1977)--8/10.
Star Wars: Episode V - The Empire Strikes Back (1980)--8/10.
Star Wars: Episode VI - Return of the Jedi (1983)--8/10.
2. Star Wars: Episode III - Revenge of the Sith (2005)--7/10.
3. Star Wars: Episode II - Attack of the Clones (2002)--6/10.
4. Star Wars: Episode I - The Phantom Menace (1999)--5/10.
Maybe I'm being stingy. Ah, George, too bad you didn't cast better actors in some of the key roles. Other complaint: stiff dialogue (seems to be a staple of many post-Star-Wars space opera productions--ugh!), which the writers of The Simpsons have also noticed (see the spoof in which the Star Wars plot is solely about bureaucratic procedure).