Art: 8/10 at the beginning and it got worse as the series progressed, so it's a 6 now.
Storyline: 9.5/10
Characters: 7/10
Originality: 9/10
Character development: 8/10
Art - I have to say that I'm disappointed in the art work. In the beginning of the series, the characters looked average with their big and shiny eyes, but as the series progressed, the artwork deteriorated dramatically and I have no idea why. In most manga the art gets better and better, but in FB it got worse. The mangaka claimed that she drew them in a way to make them look more mature, but I think she should've stuck with what she got. The characters DO look a bit older, but their eyes and the face in general just look odd now. That's not a good thing because the art is THE main attraction of manga (since it's all about visual), so it should be at top quality.
Storyline: I really like the story. The mangaka used the twelve zodiacs and applied an interesting background to it, which I think is brilliant. It has many twists in the story and each of them kept wanting more.
Characters: I think the main characters in FB are kind of dull (besides Kyo). Tohru is hopelessly naive and too optimistic and kind to be realistic. I certainly don't think anyone is capable of Tohru's pure kindness and her ability to forgive. Another one of the main characters, Yuki, is boring as hell. Aside from being a gentle and sweet guy, he is nothing more than a character that appeals to everyone in the story (besides Kyo, of course). The few impressive characters in FB are Kyo, Shigure and Akito. Kyo--being possessed by the cat spirit--has an interesting background which excludes him from the zodiac family. In the series, it shows how determined he is to gain acceptance and how he slowly overcomes his insecurity. He also has a cute personality, but his anger gets a bit over the top sometimes. And his behavior and feelings toward Tohru is just adorable :) . Shigure is probably the most likeable character in the series. He is funny, but not the cliche or stupid kind. He is funny in his unique way, as opposed to some comedic characters in other manga that just act plain dumb and irritating (which are more often annoying than funny). Akito, I must say, is a unique character that you don't see often. S/he starts off as cruel and abusive just for the hell of it, but as the plot goes further you start to see the deeper side of his/her story. Even though I don't like Akito, I certainly think s/he is one of the most well thought-out characters in FB.
Originality: Using the Chinese zodiacs and apply them into an interesting story takes a lot of creativity. I'm impressed :) Also, the transformation issue (which they transform into an animal after being hugged by the opposite gender) is quite funny, but also gets annoying sometimes (when you seriously want to see some action on Kyo and Tohru =P)
Character development: I think Kyo has the best character development in FB, some of the points which I mentioned earlier in the characters section. On the other hand, Tohru does not grow at all. At the beginning, she is already a saint. She cruises through the story being the happy go lucky girl that she was, and still the same in the end of the series. The only thing that changed about her was her devotion to Kyo, which obviously did not exist at the start of FB. Aside from gradually being comfortable with Tohru and his brother, I don't think Yuki has really developed much. He's too plain to be anything more, really.
Anyway, I think FB is a good choice if you're aiming for some comedy and shoujo. I'd say to steer clear from it if you get bored quickly if there isn't romance going on, because the mangaka spends a lot of chapters on the side characters unfortunately.