I worked at a video store on and off during the '90s and would have to say that the majority of movies that the general public loves are just mediocre, manufactured, paint-by-numbers fluff.
Totally agree with many of the movies already mentioned here but it's generally the comedies that people love that just don't work for me. Napoleon Dynamite, The Hangover, anything with Adam Sandler or Jim Carrey. I loved Adam Sandler in Punch Drunk Love and of course any of his fans I tell this to all say the same thing: "That's his WORST movie!"
But the biggest one of all for me is probably Casablanca. I don't hate it. I just don't get all the love it seems to get.