When I was a kid I read the Trixie Belden books (I will confess right here that I've never read Nancy Drew) and Hartley reminds me of her. I love her "I'll do anything to solve the crime" attitude, her fearlessness (and her fearfulness) and her inner humor. She's just a normal student with an above average interest in solving crimes and a large amount of right place, right time (or maybe it's wrong place, wrong time) luck. 
 There is so much tension between Chase and Hartley. Will they? Won't they? You just don't know. It's nice that Halliday didn't go the traditional route with them, I'm a big fan of tension. 
 Sam is still the ultimate bff, still making sacrifices to help Hartley solve the crime, except for one minor thing. Sam and her boyfriend Kyle have take their relationship to the next left: Matching T-shirts and coordinating outfits. It was funny, but if I was Hartley I don't think I could have stayed silent. 
 Hartley's mom is even funnier in Social Suicide. SMother mode was turned on early and often. Hartley also has to deal with the fact that her mom is now interested in dating, Match.com style. 
 I figured out who the killer was fairly early in the book, but that didn't make it any less good. The killer's motives were just as humorous in this book as in Deadly Cool. In both books the killer's motives are completely over the top, but it fits the humorous nature of the book.