Son was a 
mostly well-done conclusion to The Giver quartet.  
Claire is a great addition to the cast of Giver characters, she's well-developed and you really feel for her throughout her journey. 
The novel is divided into three parts: Before, Between and Beyond. Before and Between are both strong sections focusing on Claire in the community from The Giver and her journey to remember her past and learn the things the community lacked (colors, emotions, etc), but Beyond leaves something to be desired. I thought the ending was rather abrupt and a bit perplexing. The Giver and Gathering Blue were about these oppressive societies that the characters were trying to break away from and change, yet suddenly there's this big bad embodiment of evil that we have to fight  and it seemed really out of place.