Well, firstly, I think the show all sign of a good book is when you feel something. Anything at all, happiness, fear, anger, sadness. When a book has involved me well enough for me to feel something, that's when I know that it's a good book. I also believe you have to be a talented author to manipulate words into real emotions. When I read, I want to feel because otherwise I question the point of reading at all. Why do it if you won't feel anything? I like to think that's why we do almost everything in life, to feel.
Secondly, when I find myself thinking about this book for days after I've read it. I tend to consider it a good book, an excellent book at that. I want a book to really affect me and to shape me, almost. So, when it makes me think about it days after putting it down, I think that's a sign of a really strong book. I know of books that I can stop thinking about the moment I close it but it doesn't meant they're in my bad books (haha, pun) but they just don't possess this particular quality.
But all in all, I appreciate a good plot and some really awesome characters. I really love characters, honestly, I could give or take a good plot line as long as there are some amazing characters. For me, characters are what makes a book. Anyway, I'm not picky as long as a book as the bare essentials, I can make up my own mind on the rest.
What do you look for in a good book? What's the best book you've read recently?