I am a shameless reader of young adult literature. However, I realize that does not complete answer the question what "types" of books or what "qualities" within books are important to me. I would say in general that young adult books are character/personality driven. The setting, or more specifically, the situation they are in my play a huge roll in the book but the author is spending time showing how the characters act/react in response to situations and other characters -- not describing the setting or landscape in detail.
I feel that young adult books have a certain emotional appeal. This is the hardest part for me to define. As an adult I can identify with many of the emotions felt by the characters -- so I can't say that the emotional appeal to in these books is strictly limited to younger readers.
The two types of young adult books that I like the most are realistic fiction and sci-fi / fantasy that specifically tilts towards the futuristic utopia/distopia. With in "realistic fiction" my first instinct is that I like characters that are "normal" but I guess, more specifically is that I like characters that appear average yet have mental wits. I like witty writing. I like a character that is wise beyond his/her years and makes witty observations about his/her surroundings.
Sci-fi / fantasy/ utopia-distopia... well, that's getting pretty narrow as it is. But, to bring it on home -- I like books that subtly point out flaws in our society or the human condition by using a futuristic version of ourselves to show how bad we as humans could potentially mess up our world.
YA Realistic Fiction Examples:
Possibly my favorite book, (technically tied for favorite with Extremely Loud and Incredibly Close) John Green's Looking for Alaska, is a solid example for my above description. The main character collect's people's last words. This appeals to me in a literary/academic sort of way. His nick name is "Pudge" even though he's bean pole skinny -- wit. He leaves his dull public school to go live at the private Culver Creek. There he meets his new best friend and roommate, and most importantly the girl of his dreams, Alaska Young. Alaska is far out of Pudge's reach but the three friends embark on some adventures, school pranks and also ponder life's deeper questions through out the school year.John Green has written several books that fall into this description -- so far I've read, and enjoyed, all of them. An Abundance of Katherines, Paper Towns, Will Grayson, Will Grayson. I have not had the pleasure of finishing his most recent book, The Fault in our Stars.
Sci-fi / fantasy/ utopia-distopia Examples:
I've never been much of a classic Sci-Fi person. Even the adult Sci-fi books I've tried to read I never really got into. I guess I don't want to have to work too hard when reading for pleasure. I like the literary epiphanies to float like little presents into my lap -- I don't want to have to fight through descriptions of imaginary planets to get to the story. That being said... here are my favorites in this category:
Uglies (series), Among the Hidden (series), Hunger Games (series), Matched (series), House of the Scorpion.
Defining what I don't like is a little trickier. I don't like books that are boring. I don't want endless descriptions of anything really. I prefer a plot that moves along at a decent pace. I don't mind a little jumping back and forth -- different perspectives or flashbacks are okay as long as I can follow. I don't mind non-fiction biographies/memoirs as long as they more or less read like a novel. Generally, historical fiction does not appeal to me.
Some books I didn't love:
Octavian Nothing, M.T. Anderson - couldn't relate with the characters
Leviathan, Scott Westerfeld - the "steampunk" setting was not appealing to me
Before I Fall, Lauren Oliver - too much teen drama
