Tell me if you want me to be more specific, but for now I'll just say that the movie is sort of Bridget and Mark's journey to get through their insecurities over their past and future relationship.
What I really liked about the movie is that Bridget isn't pathetic, unlike in BJ2 where I found her obnoxious at times. She is more mature, though she still has her awkward moments.
The movie is really funny, moving and genuine. It is nothing like The Edge of Reason, where the humor felt too forced and Bridget was unlikable sometimes (at least, to me).
There are lots of physical comedy although
And outside the triangle, there is still Emma Thompson who really shines. She was a hoot (the promos give most of her scenes away, but there are still funny things they didn't show).
There is also a Pride and Prejudice's egg easter if you're a fan of Mr Darcy/Colin Firth. I don't know if it's mentionned in the books because I have not read them, but I found that really funny.