Eoin Colfer: The Legend of Captain Crow's Teeth
It's not as good as Spud Murphy, but comes close, and certainly grips the reader and keeps their attention.
It is focused around ghosts and spooky happenings, so probably not suitable bedtime reading for sensitive little flowers.
But it's well-written, short (90 pp), plenty of b/w illustrations, but feels like a real book. Similar difficulty level to Spud Murphy. Ds2 (6) loved it. Ds1 hasn't read it yet, but I think he will enjoy it too.
I think it would be particularly good for 6-8 yr old boys, who are just starting to read 'real books' as opposed to reading scheme books, (especially ones with older brothers).