Like Kao, I really disliked the spiders, but that my arachnophobia speaking.
I thought Radagast was hilarious, but then again, I didn't really mind Jar Jar in The Phantom Menace either. I disagree that The Hobbit was supposed to be a Lord of the Rings 4. The Hobbit was a children's book while The Lord of the Rings was intended for adults. I think Radagast's character reflects that difference nicely. Compare the first Harry Potter movie to the last, except this was done the other way around.
Whether there were boring parts in it or not, I don't know. I tend to be completely absorbed into movies when I watch them for the first time. I was sweating and breathing hard an hour into the movie. The boring bits don't really stand out to me until the second or third viewing.