From /. :

">Ewoks were cool, and Lucas hadnt sold out then.

Ah, obviously you haven't heard the back story of Return of the Jedi. No, I don't mean the bit where it was called Revenge of the Jedi. There's more.

I'll cite nothing because I have no idea where this information leaked from, and you can take it with a grain of salt because I heard it years ago. But apparently the original story for Jedi worked like this:

The forest moon isn't Endor, it's Kashyyyk. The furry friends aren't Eworks, they're Wookies. You can still see an echo of this in the final film, because the very word "Ewok" is an anagram for "Wookie" (with a couple letters dropped). No one knows why this happened, but it's a safe bet the Wookies would have been way cooler than the Ewoks were. Popular opinion has it that the merchandising for cute teddy bears was more attractive than that of Wookie action figures, but no one knows for sure. Perhaps Lucas felt burned by the negative reaction to the Wookies in the 1978 Christmas Special.

Anyway, the idea was that Kashyyyk was a slave planet. That the Empire had enslaved the Wookies was a preexisting concept, and it explainined why Chewbacca so hated the idea of wearing handcuffs in A New Hope: he was a former slave, and Han had rescued him years ago. The story of Jedi was originally to have involved the Wookie uprising. Instead we got Ewok booby traps. Also, Vader doesn't take Luke to the new Death Star. Instead, he takes him to the capital planet of the Empire, and it's there that Luke encounters the Emperor. The setting wasn't named "Coruscant" back then (that's Timothy Zahn's name for it) but Ralph McQuarrie concept art from the 1980s still exists for it.

Later versions differed from the final story in key ways as well. For example, Michael Pennington's character Moff Jerrjerod (the dude who meets Vader in the docking bay at the start of Jedi) originally had a more expanded role. At the film's climax, he realizes that the Emperor is dead and that the Rebellion is about to destroy the new Death Star, so he decides to aim the primary weapon at Endor. The idea is to generate an explosion that will destroy the entire Rebellion in one swift stroke (not to mention the Death Star and much of the Imperial fleet, but he decides that's a small price under the circumstances). This adds significant tension and makes the Rebellion's last-minute destruction of the Death Star that much more urgent.

Of course, the last story element to drastically change was the loss of the Millennium Falcon. Originally Lando does not manage to escape with the Falcon (why did you think Han and Chewie weren't on it?), making Han's last moment with his favorite ship the scene in the docking bay where Lando promises to return it without a scratch. Remember how Han comments to Leia that he feels like he'll never see it again? Originally he didn't. Lando redeems himself for turning Han over to Vader by sacrificing himself to save the Rebellion. Han loses the Falcon, but in a way this is good for his character's development because it means he finally gives up his old ways and lands the princess.

Rumor has it that they filmed Lando's death but it bothered test audiences (who do they get for these idiot test audiences, anyway?) so Lucas and director Richard Marquand decided to change it.

While I like Jedi, I've always believed that something fundamental snapped between the glorious Empire Strikes Back and the final film. Lucas lost track of what was good about the universe and the characters, and it only got worse from there."