Ring II. Please say I'm not the only one who burst out laughing at the scene where Rachel and Samara were at the well. First off, while Samara's moves were vaguely creepy, she still looked like a frog with issues. On top of that, Rachel's line about not being Samara's mother just killed any hope that I could take Samara seriously. Other than that, the rest of the movie played more like a mystery that dragged on and on than it did an actual horror movie. I really didn't feel like it was scary at all, as opposed to the first movie, which managed to actually creep me out (although it still isn't the scariest movie I've ever seen).
Also, if it counts, Dead Alive. I can't quite tell if it was meant to be a parody or if the director just got extremely lazy, but with really bad special effects and more of an emphasis on gore than anything else, the movie came off as cheesy and just disgusting, not scary. Way to fail at the zombie genre, folks.