Repetitive rhyming is great as the child can larn the words and feel like they are "reading".
Sadly as they get older its all about marketing! Erin loves those Rainbow magic fairy books which from a literary POV are pretty crappy but they have a girl's name in each title eg Holly the Christmas Fairy etc so every girl wants the one with their name. (Sadly no Erin yet) Every book follows the same pattern/story type but 6-9 yr olds love them, Erin has about 20 of th wretched things! Bu as I say to parents as long as the kids are reading thats the main thing.