Maybe you didn’t see “Titanic,” which by far the most overrated movie.
It would be difficult to choose the most overrated movie, though I’d put another Cameron film up there: Avatar. No doubt there are lots of people who think that’s a great film, but I thought it was a simplistic, heavy-handed, preachy movie, with much of the scenery copied from World of Warcraft (the MMORPG, not the film). Apart from some good special effects, I found very little to like about it.