The trilogy thats out there now (OT) is about the redemption of Anakin Skywalker and well paced. The prequal is just as well paced in it's showing of the fall of Anakin Skywalker.
The problem is alot of people, again, taking episode III as the explaination and turn to evil, when really, the entire prequal has been showing his inward crumbling from the very beginning, before he was even a Jedi. So for people that look at episode III expecting to see everything are going to be disappointed and will feel it was too fast paced, when really, this has been happening for the first two acts of a three act play. Act III is just merely the results of the acts before it.
Act I- Seperation anxiety:
Anakin's life is changed forever. He is forced to face what will become personal demons and his life is left in the hands of people who want to rear him right, but there is one who wants to use him for his own ends.
"And you, young Skywalker. We will watch your career with great interest!"- Senator (now Chancellor) Dantius Palpatine
Act II- Struggle, Temptation and Exploitation:
Anakin has been a padawan for some time. Because of his latent powers he is impatient with the progress of his training. He often clashes with his Master, Obi-Wan Kenobi in bouts and feuds.
Anakin gets alot of his opinions from Dantius Palpatine, who has been culturing Anakin on the side. Telling him what he wants to hear, what he needs to hear and instilling doubt in the boy over not just his own training, but the Jedi way. He is instilling Sith views in him, cleverly masked as matters of law and order to maintain peace and stability.
Anakin is now confused. He doesn't know what to believe as a truth of his life. Through determination he remains faithful to Obi-Wan's teachings, though the Clone War begins to tear their relationship apart.
Act III- Fear, Anger, Hate, Suffering:
Anakin's feelings and emotions have reached the boiling point and explode violently only after his main weakness is finally preyed upon by a prepared Palpatine- his fear to lose things and for things to change, his need for assurance through control and stability.
Completely taxed and preyed upon with the culmination of years of brainwashing finally taking effect, Anakin becomes desperate and falls prey and sells his soul to the devil himself.
Act IV- Depression, Justification, Reassurance:
Darth Vader (secretly hiding Anakin Skywalker) now has to deal with the aftermath of his decisions. He begins to see the results of his master's labor and his loyalties are cemented. He sees the threat and he deals with it because he believes its the only way to maintain what he wanted. Palpatine furthers the notion. Palpatine sees himself as the savior of the Republic and Anakin is having a hard time finding any fault in that.
Act V- Uncertainty, Conflict, Parental Instincts:
Having learned that Luke Skywalker is the son he thought he lost allows Vader to be more open with his personal feelings which he locked away a long time ago. The sight of his son reminds him of his lost love Padme and the baby he could never be the father of. He sees himself in his son and is instantly reminded of the path he followed which he now regrets. Too deep in the dark side of the Force to openly rebel against his Master and no longer physical able to, he pleads to his son that together they can make things right. Though he has his own agenda the dark side clouds his vision and he wishes to rear Luke the way Dantius reared him.
Vader tries to reach out to his son, which is an inward cry for help.
His son is repelled and disgusted by him however and they have a falling out. Literally.
Act VI- Introspection, Identity Crisis and Redemption:
Anakin Skywalker can no longer hide himself in the armor of Darth Vader. His parental instincts motivate his behavior. Luke is no longer a pawn to be barded with. He is his son, his flesh and blood. He is the shining light in the darkness. Forced to fight his son and make a choice that will dominate his destiny forever, Anakin Skywalker is equally forced to make a decision:
Fight for the man who saved him and is making his life possible, the man whom he owes everything now, or fight for the boy whom he never had and the joy of a daughter he never knew was.
Worse comes to worse and Luke, emmulating what his father used to be, is being murdered by the Dark Side, the same Dark Side that turned Anakin's world upside down and took away from him the one he loved. No longer able, willing or wanting to see this same evil control him and his family he makes his declaration- He IS Anakin Skywalker, a Jedi Knight and he's HAD ENOUGH!
He selflessly takes the brunt of the Dark Side's wrath, destroys his master, confesses his true feelings to his son, the feelings he's kept a secret for so long and parishes knowing he's done the right thing finally and can rest in peace with the Force.
So there we have it. Episode III is just one portion of his struggle. If you read or follow along with everything that happens and transpires then its clear and definable and nothing is missing. The saga is what it is- the fall and redemption of Anakin Skywalker.
No more, no less. The saga is complete but thats just this story arc, and we really couldn't ask for anything more.