Not the greatest thing ever, not the worstest thing ever, that's the start of my opinion of it. Like of the rest of the series.
So far in her Twilight writing (I don't know if this is true with her adult novel The Host), Meyer's been better at conveying mood than plot; I feel she was getting a good balance between mood and plot in Eclipse, the third book, and part of why I didn't like the second book New Moon was that the mood stuff, I felt, overwhelmed the plot stuff. With the fourth book, I didn't really feel the plot's import or impact in the last third. I didn't connect to it. And that's the climax of the whole shebang. Endings are tough to pull off, I know, but whatevr urgency was there, I mostly didn't "get" it.
Also, the book is maybe 200 or more pages too long. And as I felt a lot of the book was uneven, not conveying enough menace at times but then suddenly being stronger (especially when dealing with the, um, SPOILER WARNING, the pregnancy and the birth), I wanted to say Cut! Rewrite! Cut! Rewrite! This could've been a stronger, more consistently urgent book. Eclipse was. And the structure of the book is offbeat enough, with a full third of it from Jacob the shapeshifter's perspective and with some of the more extreme moments found out about after they've happened (though the infamous "imprinting" scene would probably have been VERY hard to actually show without it being incredibly creepy), that I have no idea how the potential film version of this book can get wrangled into film-shape. (And no, DON'T MAKE IT INTO THREE FILMS. Very bad idea. Diminishing returns will be the result. But I also don't know if the filmmakers can pull a Goblet of Fire and strip it down as thoroughly for film as that book was.)
There are big parts of it I like. I do kind of admire Meyer for being willing to go in a pretty extreme direction, because the book really seems to be about accepting consequences, about dealing with them as well as possible, and supporting loved ones who are dealing with those consequences. It remains a family-centric series. I like the Cullens, and can better understand the shapeshifters, too. (And Alice Cullen? Still one of my types.)
P.S. My review of the first book. Maybe one of these days I'll read and talk about Meyer's still-unfinished book from Edward Cullen's POV, see what I think of her writing in that. Meanwhile, on to reading other books.