It's not that 3D movies aren't worth watching because some totally are (see: Gravity). It's that Hollywood loves to shove it down our throat as something new and fancy and some sort of advanced technology and trendy and bullcrap like that. It's not! Most of the times, 3D movies are made just to squeeze more dollars out of us (see: any movie in 3D not named Gravity). Comic God Stan Lee explains why he hates 3D perfectly in his latest rant. [World of Heroes via Laughing Squid]
I really don't know where all the hate comes from about 3D... I love it. That being said, I don't watch 3D movies in the theater, I buy them on BluRay and watch them on my 3D TV at home... but I love it. Pacific Rim was fantastic in 3D on my home TV, just watched it Tuesday night!