On my first acquaintance with Harry Potter (following the advice of a colleague; teachers love HP, I will have you know) I was blown away by Rowling's offbeat imagination (despite large-scale reading of YA novels well into my thirties). And though I realize after the Potter-series, disappointment was a foregone conclusion - from the top, the only way is down - it was even more of a letdown that she went on to such an extremely predictable genre as detective novels.
STILL, both 'the Cuckoo's Calling' and this are charming and entrancing enough to ensure an entertaining time, although they are nothing that hasn't been done before.
Nerds like myself will appreciate Rowlings's playful use of literary references, such as Caroline Ingels ('The Little House on the Prairies') or Mr Brocklehurst ('Jane Eyre') and probably another few I didn't pick up on.
In short : Definitely not as good as Harry Potter, yet a whole lot better - thankfully! - than 'A Casual Vacancy'.