I've always found that there are different kinds of books. There are books, and then there are books, and sometimes, it's very difficult to tell what puts one book into one category or another. There are books that may be called "bad" because of the low quality of the writing, in one way or another, and then there are books that may be called "bad" just because they're not your cup of tea. I try to distinguish clearly between the books with serious flaws in construction and the books I'm just not that into, but that's not what I'm thinking about right now.
What I'm really interested in is what makes books books. What thrills the reader, what makes a story memorable, what turns a book into a comfort book - basically, what makes a reader passionate about a book.
I write of this now because I've been doing a fair amount of rereading recently. Specifically, I've been rereading Sharon Shinn. Now, not everything that Sharon Shinn writes is flawless, but I have been more than impressed by two series she's written: the Samaria series, and the Twelve Houses series. And at times, I've been hard pressed to determine exactly why I'm so impressed by them, why I'm so passionate about them I've read each book in the series at least three or four times, why I've put these books on my MUST BUY list. (You know, for when I have money.)
These books aren't flawless. They're well written and well constructed, but the book critic in me can identify plotting discrepancies, characterization issues, etc. etc. But I love them anyway. Why? The Twelve Houses series has some of the most enjoyable characters I've come across in fiction, characters I'd just love to know/be in real life, and I find the world building simply excellent. The Samaria series I like in part because the premise is just so KICK ASS AWESOME. Although I'm sure, given its religious undertones, some people might not like it quite as much. But this still doesn't explain exactly why I love them the way I do.
The 'why' is probably something that varies from reader to reader, and even in the same reader, something that varies from book to book. So what does make a book a book? One of my former roommates has a pet series of her own, the Trade Pact Cycle by Julie Czerneda. She openly acknowledges places in the series where the writing is a little off, where the characterization is just weirdly wrong, and yet she loves those books passionately, and sometimes swears by them. (I read them too, and found them entertaining and well-written, though not quite books I would be passionate about.)
So what is it? What makes a book a book, one of those buy-ten-copies-in-various-editions, read-twenty-times, gush-about-forever kinds of books? I'm really not sure, but I really think that's part of what reading's about: finding those true book loves, and maybe feeling a little more complete for having them.