I think it's a shame Lucas didn't take this as an incentive to let other do the directing from here on.
Well, he did get Richard Marquand to direct Jedi. I suppose he wasn't as happy with that result.
1. The Empire Strikes Back - I love the epic feel of this movie. The developing relationship between Han and Leia is well done. The duel between Luke and Vader is great. I love how Luke charges in swinging his lightsaber with both hands, while Vader casually uses his with one hand. This one also has the best dialogue in the series.
2. Star Wars - Truly a classic all the way around. Not much else I can say about this one.
3. Revenge of the Sith - Lucas bridges the two trilogies very well here, I think. The fall of Anakin was well done, and I especially love the final showdown between Obi-Wan and Anakin. Great acting from Ewan McGregor.
4. Return of the Jedi - I think this film is sometimes unfairly maligned. The Ewoks don't bother me (I like the contrast of the cute little primitives defeating the big evil technological Empire). In my opinion, the battle above the Sarlaac is one of the best action sequences in the series (helped by the great Williams score, no doubt). The inner turmoil Luke endures during his final battle with Vader is great, and Ian McDiarmid gives my favorite performance as the Emperor here. I'll confess, when Anakin replies to Luke's promise to save him with "You already have, Luke. You already have," I get a little choked up.
5. Attack of the Clones - Another one I find to be underrated. I really enjoyed the political aspect of this storyline. Plus, Christopher Lee.
6. The Phantom Menace - The weakest story of the series, but I still find it worthwhile for the Podrace and the duel with Darth Maul.