There are too many awful films to list, so I am going to apply the tag "overrated" only to films that won the Best Picture Oscar when they didn't deserve it. (This is, of course, a highly subjective assessment).
I would include:
An American in Paris (beat A Streetcar Named Desire)
Around the World in Eighty Days (over Giant, The King and I and The Ten Commandments)
A Beautiful Mind (full of errors, yet it won over Gosford Park, In the Bedroom and Moulin Rouge)
Braveheart (I would have chosen Sense and Sensibility. Even Apollo 13 or Il Postino)
Broadway Melody (yawn)
Cavalcade (further yawn)
Cimarron (yawn, again)
Dances with Wolves (over Goodfellas)
The Departed (the least of the nominees. Even Little Miss Sunshine would have been a better choice)
Driving Miss Daisy (over Born on the Fourth of July, Dead Poets Society, Field of Dreams and My Left Foot)
Forrest Gump (Shawshank Redemption was robbed. Don't get me started...)
Gigi (beat Cat on a Hot Tin Roof)
How Green was my Valley (over Citizen Kane?! Really?!)
Kramer vs. Kramer (two words: Apocalypse Now)
Oliver! (The Lion in Winter? 2001: A Space Odyssey (which wasn't nominated))
Ordinary People (over Raging Bull, (sigh))
Shakespeare in Love (Elizabeth, Life is Beautiful and Saving Private Ryan were all more worthy)
Titanic ('nuf said)
I would have a tough time deciding between Titanic and Forrest Gump, but I will give the nod to Titanic because the sheer volume of its wins amount to greater overrating!
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--James