Don't get me wrong, I really like all six main Star Wars movies, but ROTS is my least favourite.
Because you know how it's going to end, the plot was rather predictable. And this is hard to explain, and is probably just me, but to me it felt like I was watching something closer to historical fiction. Like, an artist's rendition of the historical events of the fall of the Republic and rise of the Empire. Rather than have much emotional depth, it was just giving us the facts about "what really happened when the Empire came to power".
That said, the novelization of ROTS is my favourite Star Wars book. Stover does such a good job at building the characters, and the emotions, and everything. I loved that book. It also confirmed one important detail that all other sources seem to miss: Dooku knew that Sidious and Palpatine were the same person. Other sources never show that.
My favourite prequel film is actually Attack of the Clones. Fun science-fictiony adventure, the building romance while it was still pure (without all the jealousy), and great characterization (the devoted Senator, the brash young man leaping head-first into the world, the father-figure who is not at all prepared to deal with his son, etc.)
My film order (starting with the best): 5, 4, 2, 6, 1, 3. But again, they're all good. Just because Episode III is last, doesn't mean it's bad. It's just 7/10 over Episode V's 10/10.
-Sparks Nevada, Marshal on Mars
"Who cares what evil lurks in the hearts of men!"
"Unless evil's carrying the Martini tray, darling."
-Frank and Sadie Doyle