In his recent entries, "ROTJ is a Joke" and "ROTJ is a Joke part 2," Grandmaster of the Jedi argued that the Ewoks had a negative impact on Episode VI. In the interest of showing both sides of an argument, I will now present the other perspective on the issue.
Some aspects of Return of the Jedi leave something to be desired. However, as the film is now over 22 years old, it's to be expected -- as it would be of any movie. I'm not saying that this sixth and final installment of the Star Wars saga is perfect. I'm just saying that
Jedi may not be as bad as some believe.
As I mentioned in the introduction, most of the accusations center around the Ewoks.
Grandmaster of the Jedi has summed them up quite nicely, and any reader of this would benefit from reading his entries first (see links above). At one point, the Grandmaster points out that, at one point, the ROTJ battle was to be Wookiees versus the Empire, but points to lack of technology as the reason this idea was rethought. While that likely played a role, I think there's more to it than that.
It is my understanding that a low-tech versus high-tech battle of a primitive species versus a galactic empire was proposed from the very beginning, when the original Star Wars was still far from its final form. At that point, three decades ago, George Lucas - still a relatively unknown filmmaker in the industry - didn't have the means for such a battle. However, liking the Wookiee design featured in those early ideas, he took it and made it a single character: Han Solo's co-pilot.
Six years later, while working on
Jedi, the concept resurfaced. At that point, I believe it was feasible. However, by placing Chewbacca as the copilot of a speedy space freighter, Lucas had established the Wookiees as a technically-savvy race. So, it became the (quite similar) Ewoks who took that role.
See, the battle is unfair by necessity. The whole point is for it to be vastly weighted in the Empire's favor. As the Grandmaster briefly mentioned, it shows the power for an underdog to defeat the establishment. In many ways, it resembles Lucas' own rise from obscurity and his fight against the Hollywood behemoth.
However, believability is still necessary. And so I move on to analyzing as to how the Rebels managed to destroy the shield bunker that fateful day.
The Imperial troops who were sent to ambush the Rebel strike team were supposedly the Emperor's best. However, they were anticipating resistance from only those select Rebels. If the fight had gone that way, then the legion defending the shield generator would be overkill. It's the surprise assistance of the Ewoks that turns the tide of the battle. The Empire was caught by surprise, off-guard and ill-equipped to face this new threat.
The heart of the issue, though, is that audiences question whether Ewoks can be a threat at all. They may say that the Ewoks are not natural warriors and lack experience. That have been isolated on Endor all their lives. While that may seem significant in the GFFA, we humans have never left our planet, and yet I daresay we have had plenty of experience in battle. Judging by their armament, the Ewoks probably have about the technological prowess of cavemen, but they are apparently significantly more advanced when it comes to pure intelligence: the Ewoks' tactics center around traps and turning the Empire's own equipment against them. It is clear that they benefit from past encounters with foes native to Endor - see the Ewok movies and cartoons for examples.
One of the most important advantages that the Ewoks' guerilla-style approach reaped was the theft of an Imperial AT-ST. The walker that Chewbacca and his furry little friends captured -- realistically enough, by the way -- played a huge role in the battle. It brought massive amounts of much-needed firepower to the Rebel cause, and became
the technological force in the battle once the other AT-STs had been eliminated. That single walker could practically win the whole battle by itself. One could see it as a metaphor for the Empire's -- and, before that, the Republic's -- rot-from-within downfall.
The Battle of Endor is a symbolic fight. It epitomizes the conflict of good-vs.-evil that spans the entire saga; it crunches it all down into one crucial battle at the epoch of the Galactic Civil War. It may not be perfect, but it's certainly not as bad as some think. Its biggest flaw is the somewhat outdated visual effects, but even those are impressive considering the age of the movie. Furthermore, the effects could theoretically be updated in a forthcoming edition of the movie. Still, the effects aren't the point. The point is the triumph of the underdog against the dominant power, the I believe the Battle of Endor shows that quite well.
To parrot the closing thoughts of the Grandmaster's first installment, perhaps I've kindled the fire to a new generation of Ewok defenders. More likely not.

Still, please feel free to leave your thoughts, and thank you to the Grandmaster for opening this discussion.