A thread on the Star Wars saga has already been done, but i'd like to put in my two cents on the matter.
1. The Empire Strikes Back - It goes without saying. Not since Frances Coppola's The Godfather Part II has there been a sequel that stands alone as a separate work from it's predecessor. The end result in Empire is now a standard in any sequel: the bad guys get the win, leaving our heroes to regroup, lick their wounds, and get ready for the next battle. Billy Dee Williams as Lando, and the majestic Frank Oz as Master Yoda are the standouts of this dark, thrilling chapter of the saga.
2. Revenge of the Sith - Lucas saved the best of the Star Wars prequel trilogy for last - and with it, the series itself. After the silliness of Phantom Menace and the dreadful love story that was Attack of the Clones, George goes for broke, adds the elements of what made Episode V a classic, and goes one better - he makes the last hour of the saga from exciting, sci-fi fare, to Shakespearean tragedy as Anakin succumbs to the Dark Side and becomes the evil Darth Vader.
3. A New Hope - Of course, this also goes without saying. Episode IV was the film that started it all. The reason why generations of adults geek out whenever we hear John William's timeless opening theme on television.
4. The Phantom Menace - Episode I gets so much shit from the fans, and to a good extent, the fans are right on: Its the silliest of the lot and it includes the worst character since the Ewokes in Episode VI with the awful Jar-Jar Binks (George Lucas, what the hell were you smoking when you brought this blubbering idiot to life!?). But Phantom Menace, I now realize, wasn't supposed to be made for the old-time fans. This was made to bring in a new generation of Star Wars geeks who'll dress up in Jedi and Clone-trooper outfits every year at Comic-Con in San Diego. Plus, it was fun as hell to watch Darth Maul whip out his double-headed lightsaber and cause havoc for the Jedi.
5. Return of the Jedi - Much like The Godfather Part III, we went in with high hopes and ambitions that the final installment would do one better than its predecessors A New Hope and The Empire Strikes Back. What we got were primitive teddy bear warriors and a party on their planet after the Emperor and his second Death Star are destroyed.
6. Attack of the Clones - The worst one. I hated how this became a sappy, romantic melodrama in space, rather than a mysterious, dark insallment of how Palpatine plays both the Jedi Knights and the Separatists as pawns in his quest for galactic dominance. Plus, Hayden Christensen (sp?) made Anakin a whiny, annoying bitch, rather than a doomed, though sympathetic figure. Not even credible actors like Ewan McGregor, Natalie Portman, Christopher Lee, and Samuel L. Jackson could save this pathetic installment from going up in flames.