Avatar - it was Pochahontos with blue people. The dialogue was poor and predictable (I didn't sign up for this - cliche thank you) and not to mention Cameron is tremendously over rated. Yes, it cost a lot of money but it's quality and not quantity.
The Matrix - I find the idea fascinating however I've seen better acting, superior directing and dialogue. Fascinating but definitely too hyped.
I didn't really mind Titanic or The Godfather films... I can see why some people don't like them. The Titanic was abit too much about the love story for a lot of people and The Godfather was too long with too much talking. Most of the highly rated films that come out now are awful... The last film to come out that I actually enjoyed was No Country For Old Men.
The Harry Potter franchise. I love that allegedly JKR fell out with the producers, and so deliberately made the later stories unfilmable. Other than the first they make no sense stand alone, and unless you bring in a whole lot of context (like having read the series, and knowing what is supposed to be happening in advance) they are borderline unwatchable.
Loved the Matrix because it was a new idea to me at the time and well executed. As the series went on, and the new age stuff got trowelled on deeper and deeper in was only the action sequences that were worth watching.