I would generally agree that ROTS improves somewhat the two earlier prequels. Anakin's final descent into the dark side is made more poignant when we remember what a precocious little kid he was (even if he was played by one of the most annoying child actors in history). Also, we can clearly see the line tracing back to the "Phantom Menace" to which the title refers (even though we really knew all along). But nothing can excuse all three films' stilted dialogue and awkward love scenes between Portman and Christiansen.
On a grander thematic level, considering the "PT" as a whole, I can see Lucas' larger point about politics. It is really that intrigue that leads to the downfall of the republic. The details of the intrigue, i.e. trade disputes and tax imbroglios, are largely irrelevant -- made especially clear in ROTS when the leaders of the trade federation are summarily laid to waste by Anakin. The emphasis on such Byzantine political detail is in marked contrast with Episodes IV-VI. It is interesting that the Emperor himself does not appear in Episode IV at all -- he was mentioned during the early scenes as I recall when it was announced that the emperor had dissolved the senate -- so in one throwaway line, Lucas almost completely discards the political issues of the prequels! Why did we not get to see a scene in the Senate with bizarre looking creatures from various exotic planets flying around in their little pods, protesting the Emperor's extreme measure??? Because politics has served its purpose and is no longer important to the story.
Moreover, when viewed together, the prequels show how the good side of the force has failed. Palpatine's shrewd seduction Anakin emphasizes in contrast the impracticality of all the mystical, ethereal non-sequiturs uttered by Yoda, et. al. throughout the prequels. In this way, it also ties in nicely with Episodes IV-VI in which Luke's more "down to earth" way of learning the Jedi arts (despite Yoda's esoteric ramblings to him) are really what defeat the Emperor. In the climactic duel between Luke and Vader, it is Luke's anger (as noticed by the Emperor) that defeats Vader. The original Jedi would never use this method. Despite his mixing of dark and light elements of the force, Luke will "never turn to the dark side." Obi Wan's response to Anakin that "only a Sith deals in absolutes" thus seems an ironic foreshadowing -- it is the Jedi's own failure to see beyond absolutes that leads to their inability to stop Anakin's downward spiral -- but it is Luke's ability to transcend Yoda's absolutist Jedi creed that ultimately brings Anakin back from the dark side.
Overall, even though ROTS is not the perfect movie, it has reinvigorated Star Wars as a cultural phenomenon beyond its core audience. I don't find it surprising that younger fans tend to dismiss the original Star Wars. To those who did not live during that time and have come of age with all the Sci-fi blockbusters that have come to proliferate the cineplexes, the original does look a bit dated and, of all the Star Wars movies, it was the most badly edited and schlocky looking (which also gives it a degree of charm). But speaking as someone who was a part of the initial craze in 1977, the movie was breathtaking for its time and created a true revolution -- for those of us who lived through those times, the final scenes of ROTS are quite emotional and do tend to complete the circle that started in our now dimly remembered childhoods. In this way, Lucas has truly succeeded.