The novel of Revenge of the Sith is canon. It aligns with the established Star Wars canon framework and adds depth and detail to the events depicted in the movie of the same name.
The plot of Revenge of the Sith centers around the final stages of the Clone Wars and Anakin Skywalker's descent to the dark side. It's a complex and intense story with lots of action and drama.
One of the main themes is the fall of Anakin Skywalker. His journey from a Jedi Knight to Darth Vader is central. Another theme is the collapse of the Republic. The political intrigue and manipulation that lead to its downfall are explored. Also, the theme of friendship and betrayal is there, as Anakin betrays his friends and the Jedi Order.
Definitely Anakin Skywalker. He's the one who goes through the most drastic change. Then there's Palpatine, the mastermind behind the Sith's plan. Obi - Wan Kenobi, who has to face his former apprentice. And Yoda, the wise Jedi Master who tries to counter the Sith's plot. Also, Padmé, whose love for Anakin is a key factor in the whole drama.
One idea could be exploring what would have happened if Anakin had a different mentor during his fall to the dark side. Maybe a Jedi who was more in tune with his emotions could have guided him better.