Surprisingly good, with movies like this I'll hold back on writing off Will Ferrel altogether.
What carrys this is the quality of the music, its almost believable, but just not quite right. Really well done. Another very under rated and under publicized film. This is what a parody film should be. Its depressing that some people simply don't get it, they must be exceptionally boring individuals. Its predictability and cornyness are certainly not negative points.
As usual with this sort of film the main characters are fairly stupid. Nice how it mixes it up in the second half. Ending a bit Hollywood, the original ending as on the DVD would have been better, in the hospital. You know that they are fighters and you saw the plan so you can assume they'll work it out sooner or later.