I just finished the trilogy and I must say I was blown away.
From a very simple premise - young innocent girl may be 'more' than she appears, and so much more than she may know - we get a phenomenal buildup from Australia to Prague, Barcelona, Heaven and Hell, from intimate relationships such as deep friendship, brotherhood, kind fathers and of course, EPIC LOVE. We move through history, theology, the deep seedy underworld of crime and sin, battles that unite the world, and the battles that rage silently in all our hearts.
I must say I was constantly surprised and impressed by the twists, expecting a humdrum ride of YA tropes. As the story moves forward, the backstory subtly weaves itself in at a perfect pace. Characters grow and change, make mistakes, apologize, get to fight another day.
I started book 1 a few years ago and stopped after a couple of chapters because I didn't see where this would go, and I wasn't into yet another innocent teenager as a protagonist. I was wrong; the story has enormous breadth and width and depth, and absolutely delivers on its promises, which is pretty amazing when you consider that god, Lucifer, all the angels and demons are characters.
I'm really glad I picked it up again! It turns out I'd stopped reading Luminous literally 3 pages before things start happening - and they don't let up after that...!!