Pretty bad. Not horrible, and Colin Firth is entertaining to watch, but come on... Where do I start... Ok, I have problems with the story: an upbeat musician woman living in New York is celibate for 17 years, pining for a guy she left and she knows won't come for her? Give me a break. Also, the guy is engaged, but we never see him having any affection towards his fiancee. That's unrealistic as well. Going on: the main character girl and her mother look from the very beginning "rich" - expensive hair highlights (waitresses can't afford those), and then the girl keeps going on shopping sprees when in London - that's privileged behavior, there is no way she grew up the way they are trying to portray. Also, Amanda Bynes was really bad for that role. Even if the "daughters" were switched, the casting would have been better. Amanda Bynes is dull, unbelievable as a new NY working class girl, unbelievable as a daughter of a musician, and as a poor girl who finds herself in a fancy castle. Then, the "boyfriend" - he would have been ok, but why oh why did he have to be "born privileged"?.. He could not be a simple boy? The makers of the film could not fathom that a "cinderella" could like a regular kid? This makes me sad. If I were a black person, I'd say this whole film reeks of White Privilege. Except, I am white (and don't believe in White Privilege), and this film just reeks of privilege - the way "poor people" are portrayed is super unrealistic, and the fact that the "regular boy" had to be secretly half-royalty is deplorable.
Now, here is another thing that makes this film bad. It's giving false hope to all those abandoned daughters who grow up idealizing their fathers who are never ever there, and are out somewhere busy with their careers and with marrying other women (yes, I am one of those fatherless girls). The thing is, the fathers NEVER come around, and I can say that now. You wait and wait, and it just does not happen. Ever. The father would be pleasant to you at the rare occasions when you meet with him - once per five years or so over the decades - but he will NEVER be there for you. There is a good film "Dirty Girl" that shows the realistic side of this. And "what a girl wants" sucks. And, it plays to the dream of all kids of divorces that their parents would end up together. They won't and this is cruel to feed this plot line to all those kids.
The only good thing about this film is the name.