Watchmen...a good portion of the movie actually. I wouldn't necessarily say "ruined" but it was definitely p!ss poor choices. Particularly the funeral scene accompanied by Simon and Garfunkel. The Comedian getting his @ss kicked to "Unforgettable". The Comedian and Night Owl calming down a riot to "Boogie Man". Horrible, cheesy and overly cliched.
The backing music in the Dr. Manhattan sequence was perfect I found.
While I have significant problems with the movie version of Watchmen, I think the opening set to "The Times They Are A-Changin'" is incredibly strong. "Unforgettable" has an important meaning in the original comic, so I'll let that one slide.
Not to hijack, but here you go: