You know, I'm really quite surprised not to find any fans of the books here.
It's really the kind of thing I think many Terry Pratchett fans would like.
I'm a bit rubbish at reviewing things, but here's a link to a load of Goodreads reviews. http://www.goodreads.com/book/show/1130 ... g_Sequence
Here's my take on it anyway.
The series predated Harry Potter by a good few years, but has some things in common with it. For example, the main hero in it is an 11 year old English boy who discovers at that age that he is a wizard (or Old One in the terminology of the series). The series is a story of a prolonged battle by the 'Light', a supernatural order of incognito theoretically immortal beings to prevent their evil counterparts ('the Dark') from rising and taking over the world and the hearts of humanity.
I think it's great. Magic, elements drawn from British mythology (the Arthurian aspects really appealed to me as a child), time travel, and some very mature recurring themes for the intended age groups (notably love and betrayal, and the need to sometimes do terrible things in order to do 'good').
It feels much more 'adult' in tone to me than the Harry Potter books (though I did like them).
Anyway, I recommend it.