I think that especially with kids, anything that gets them reading is good. My little brother did not read for fun for years then all of a sudden discovered reading---and his first self-chosen book was Shogun, which is like 900 pages long. We all were stunned.
Personally, I really hate literary snobs. I took a creative writing elective in university which was taught by such a person and it was a miserable experience. I was far too 'genre' for her, and she critiqued all of our work with a fervent belief in literary fiction as The One True Way. It turned me off writing for awhile. I spent a solid year reading nothing but fanfiction after that.
The thing is, people can like all sorts of different things. My mom reads her share of literary fiction, but she also enjoys those sprawling romance sagas from time to time because they are very long so she can go to Florida for a week and only need to bring one book with her. If you are going into the bookstore to browse and THAT is your selection criteria, Ondattje is not going to cut it. But in another circumstance, it might be something you enjoy. And within the genre of 'sprawling romance saga which will last a whole week on the beach' there are authors who do it better and authors who are less sought out...
Personally, I did enjoy the Harry Potter books but I found Twilight completely ridiculous. I am not the target audience for it anyway. But I am sure even within the genre of Books Which Appeal to Teenaged Girls there are the better authors and the not as good, and I am sure there are some very well-read 14-year-olds who hated the Twilight books. Thankfully there are enough books out there for everyone, so why be a snob about it? Let everyone enjoy what they want.