I finally watched this movie! Glad I didn't make it to the theater to see it; if I'm gonna cry over a movie, I'd rather do it alone on my couch in the dark LOL. I liked it, though. I thought it fit the book well in most instances. They did leave some things out, obviously, namely the whole Julia/Campbell subplot (which I didn't care much about in the book anyway) and Jesse's pyromania, but most of the other things I remember from the book were there, and of course they added some things too.
I do veto the change in ending... Even though I'm still a little torn over how the book ended, it was certainly more interesting and completely unpredictable, albeit even sadder than the movie. Knowing how it really ends, I found the ending of the movie kind of unsatisfying and just very cliched. But other than that, I liked the movie. I thought it was well cast and well acted too.
It did seem like Kate got a lot more screen time than Anna, though, which kind of changed the whole theme and message of the story. Like Mare said, it seemed more like it was the story of everyone coming to terms with Kate dying, rather than than being so wrapped up in Kate that they ended up losing the other daughter.