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Bad? Well, the top 250 of the IMDB is perhaps the best film list ever made. Why? Because its fully democratic nature and its voting system means that every film with more than 25,000 votes has a chance of appearing on the list, so popularity beyond a certain threshold is not required.
Among the highest ranked films of the list the ones that I watched and personally didn't like very much (gave a 6/10 or less) were:
25. Casablanca (never understood it, maybe because it has a certain cultural appeal to americans). (rated it 5/10)
56. Toy Story 3 (quite mediocre and formulaic) (6/10)
65. The Intouchables (very medicre and formulaic film: a mediocre film for mediocre minds, as an IMDB reviewer put it). (5/10)
79. Chinatown (boring) (5/10)
118. The Seventh Seal (boring, lacked the drama of other Bergman films like Cries and Whispers) (6/10)
126. The Hobbit (again, it will fall out of the top 250 like Avatar did previously, I think that movies should have a 1 year cooldown after release before they could become candidates for the top 250) (6/10)
Overall, I didn't find anything in the top 250 to be really, really bad. Like Battleship and the Transformers movies. Usually I found these movies either boring or formulaic, but well executed nonetheless.