This is not to say these are bad books. Characters are like real-life people, and the people (real or imaginary) I want to hang around with may well be people another person cannot stand. And that's fine.
But when I'm reading, I want to care about what happens to the characters. I can forgive a lot of flaws -- clunky writing, melodramatics -- if I care about the characters. Just glancing over the fiction shelves here at Rancho del Cozy, as I look at the book titles I remember the characters. I remember hoping things would work out for them and being happy for them when things went well (and saddened when things didn't go well). The most memorable books are ones when I either want to break the fourth wall and go in and save characters who didn't make it, or ones that after I had closed the book cover and moved on, I would think, "Gee, I wonder what ever happened to so-and-so?"
This is not to say that the characters always have to be likable. You don't have to want a good outcome to care about the characters -- in a way, thinking to yourself, "Ye gods, I hope character X gets what's coming to him" is caring about him.
If I don't care about characters in a book I'm reading, I at least have to be interested in them. The one disappointment I had when reading Cormac McCarthy's Blood Meridian was that I didn't care about the characters, though I was deeply interested in and fascinated by Judge Holden. But The Kid didn't move me or interest me much. However, McCarthy did give me characters I cared about in The Road, which makes it one of the few books I've read that's brought me to tears.
Your milage may vary, of course, but here are some of the books I've read that featured characters I cared about.
Cavedweller - Dorothy Allison
The Road - Cormac McCarthy
The Robber Bride - Margaret Atwood
The Clan of the Cave Bear - Jean M. Auel
L.A. Confidential - James Ellroy
The Crimson Petal and the White - Michel Faber
Boys and Girls Together - William Goldman
A Song of Ice and Fire series - George R. R. Martin
Lonesome Dove - Larry McMurtry
Harry Potter series - J. K. Rowling
Blonde - Joyce Carol Oates
The Terror - Dan Simmons
The Kitchen God's Wife - Amy Tan
The Shipping News - Annie Proulx
The Stand - Stephen King
The Shining - Stephen King
The Painted Veil - Somerset Maugham
The Hotel New Hampshire - John Irving
Watership Down - Richard Adams
The Accidental Tourist - Anne Tyler
And now I'm at work on a new book, and it's time to not only get to know a new set of characters (or "imaginary friends" as I think of them) but to make sure that the readers care about them as much as I do.