I have to say that Flowers in the Attic is a masterpiece. V.C Andrews was a genius, she presents flawless imagery and circumstances that really draw you in.
V.C's writing style has a lot of heart. The best points are the buildup of Cathy and Chris's relationship. The character of Corrine and Grandma Olivia serve their purpose well as villains (Although Corrine is more on the unintelligent side rather than "evil" though). Overall, it is the atmosphere the book creates that really draws you in!