DS seems to like books that a part of a series. He loved Narnia, and he is really enjoying Alex Rider, but has got to book 7 of 12 and is losing a bit of interest.
He isn't a strong reader, probably about average for his age. We are past needing pictures (no not 13th storey treehouse) but doesn't like very long books as he only reads a chapter or two a day, and long books take too long to finish (eg most of the David Walliams are way too long for him to read to himself).
He finds Harry Potter too challenging, but we read the large hardback illustrated books together.