Let's see. I think I'm the only one who disliked the Chronicles of Narnia, but that might've been because I had just finished the glorious series Harry Potter. Narnia was shallow, and I felt that the world wasn't developed properly. (I think someone else agrees because I saw a discussion about the CoN series a while back, but I'm not sure.)
I dislike books like "Gossip Girl" in genderal.
I dislike hyped-up vampire books, although some of them are really good. I wish more people had @Sashira's talent at writing vampire. Anyway, for the horrible vampire series books award I nominate: The Vampire Diaries and Twilight. The characters are just flat and plain - out boring.
More on Twilight: It's not very well written. It also sends the wrong message to young girls, basically teaching them that they should throw away their life and marry some guy at eighteen. Like our only goal in life is to marry, have babies, and let your husband do all of the work. No. Just no.
Eragon also wasn't that great. It had bad grammar and big words. And it's kinda dry.
However, (going slightly off-topic, but whatever) some books I liked have been ruined by the movies: LIKE THE GREATNESS THAT IS PERCY JACKSON!!
(Prepare for rant.)
The movie literally has the characters 4 years older than they are in the book. Like, if going by the book, Percy at sixteen already defeat Kronos. And the second movie is what, three years later? WTF is this? I'm actually really glad it was discontinued. Secondly, they don't add in the prophecy. No, Percy just goes off on a random quest, and Annabeth tags along. But guess what? It gets worse in the sequel. They actually go into the belly of the beast and have to escape. Pinocchio rip-off. I don't want to get into too big of a rant, but I have a lot to say. Sorry if that was hard to follow, but what I'm trying to say is that YA movies could also be handled better. Well, that, and I'm telling the Director of PJ to have a look at how the director of HP handled things.