I have liked quite a few mainstream blockbusters. I've liked a lot of books that have been turned into movies, like Girl Interupted, One True Thing, It and Bridget Jones.
Being that my husband and I read so much we usually get books as gifts, some of the less avid readers in our family stick with the topsellers at the grocery store. I can count on a Stephen King book from my mother-in-law every year, I always read them and yes, I sometimes like them.
I also read the Harry Potter books, I started long ago when my younger brother first started reading them, we were so happy he was reading anything that the whole family decided to read it and now I'm a bit hooked. I don't think they are great but I like being able to discuss books with my little brother and now my son who is just getting into the first one this year.
I don't see anything wrong with just enjoying a story, whether it was written well or not, sometimes it's good just to breeze threw and not have to think too hard about it. And a lot of my mainstream books have pointed me to more accepted classics, like Girl Interupted mentioned Kafka and so it sparked an interest and I picked up some of his books.