Breaking Dawn was, in my opinion, the worst book in the series. Frankly, I'm not a huge fan of the Twilight series, but I don't exactly hate it.
I just don't really like how cliche everything was. Bella got her wish of becoming a vampire, Jacob found someone to love/imprint on (of course it just had to be Nessie, who Bella miraculously conceived), and other things like that...
It's an okay book.