I also disliked the Power of One when I had to read it for my senior year AP English course.
Other books I disliked:
A Prayer for Owen Meany made me cringe, a lot. It has the great dishonor of being one of the only books that I ever just...stopped reading. I eventually forced myself to finish it (I had to, it was assigned reading, although the way the class was structured I could go through the books whenever I felt like it) and I didn't like it any better for doing so. The themes in that book were very hard to handle for a high school freshman, and I just didn't enjoy the story.
Marrion Zimmer Bradley's The Mists of Avalon. I despised that book - it's a female-centric retelling of the Arthurian legend cycle. I was going to say feminist, but it's really not. The women aren't empowered, just enamored of their menstrual cycle and having babies.
Any of Andre Norton's older work. Her more recent novels are good, but her early stuff is written in the most ponderous, formal fashion.
Dennis L. McKiernan's Iron Tower series. Admittedly, it was intended to be a sequel to the LOTR series, but when that permission was denied, he just kind of changed the names of things, and it's still obviously extremely derivative, and quite frankly, I can't blame Tolkein's estate for denying him the rights to release it as part of the LOTR series, as his writing is awful.