My kids did/do not like them, for different reasons. By and large, they are very popular and most kids do like them.
For dd: she is gifted, and learned to read on her own when she was 5. She very quickly was reading at an advanced level, and had no patience for "learn to read books" except Dr. Suess. She was too young to appreciate some of the themes in books for preteens, so she preferred richly illustrated fairy tales and the like. If you look, you will see many use complex sentences and rich vocabulary, and rely on pictures to help get the meaning across to young kids.
Ds is now 6. He struggles a bit with reading, but loves being read to. He is just at grade level right now, but he just doesn't like reading. He's impatient with himself and can't follow the meaning well when he's trying to sound out words. He doesn't like these books because on the one hand they don't have enough pictures, but on the other hand, the language is too simple for him. They really are meant for kids to read on their own, and the thrill of being able to I think makes up for a bit of what is lost in richness.