Summer final episode was absolutely surprising with lots of unanswered questions for sure. Choosing Cece as A was not such a bad idea with some supported flashbacks which are connected to some reasons however according to the story that Cece told to Ali, all the A game starts after she hit on Ali. But Ali started to get anonymous messages way before the hit. So someone had already started the game before Charles. Even Alison started to dress up as Vivian to spy on A.
We also still don't know how Mrs. D died, who murdered her, how Sara and Cece met, why Wren helped Charles in Radley, etc.
Charles is probably obsessed with Alison because when he was a kid he used to feel like a girl but was not allowed to be one. When he became he had no family and Alison was one and only beloved daughter in the family. Maybe that's why he might have attacked Alison in D house.
Although A as "Cece" makes sense, there are holes in the entire story. But Cece definitely interested me more than any other possible A guesses. I'm not sure whether continuing to the serial will work. PLL team should fill lots of blanks in the following seasons. Still less disappointment than HIMYM final episode.