A brilliant book, for a chapter or two, then it falls apart and becomes another boring description of how a middle aged man, Dino, gets obsessed with a young women (or old child, as we "follow" Cecilia between 15-17 years). The first pages are however worth reading as the description of detachment, boredom, is exceptional. The inability to connect to the world and at the same time be aware of the situation as someone observing the situation is a very interesting situation that most people have experienced.
For some reason Moravia slides over to define boredom more like restlessness without reason and all of a sudden the depth is lost. He spends the rest of the book like a 12 year old obsessed with the girl next door, with about as much reflection and sophistication.
Not even the relation between Dino and his mother is explored, something that could have been interesting from a class/privilege perspective. Why he do not dare to leave everything and cut the umbilical cord to his mother is never explained, it is as if Moravia is afraid of really testing his idea and character.
When he first start to meet Cecilia there are some interesting situations, but Moravia refuse to reflect and seem more interesting in exploring the sexual relation between Dino and Cecilia than anything else. If this book would have been written in the 19th century, or at least before Lolita, it might have been able to contribute to something interesting.
So take the time to read the first two chapters and then spend time on something more interesting would be my advice.