I know SP fans' opinions are divided about this book. There is one thing that is clear: from this book onwards, the series takes a very obvious turn to the dark.
There is still banter, there are still a lot of very funny moments, there is plenty of comic relief, there is budding romance ... and there is a clear shift towards darkness. Not just darkness embodied by flag-waving, moustache-twirling villains and evil ancient gods, but a whole different sort of darkness, one that is in all the characters themselves, and one that we're starting to see glimpses of.
So yeah. Some people don't care for that, some people love it. Dark Days
is - quite possibly, and this changes depending on the day and my mood, but most of the time - my favourite of the five books out so far. And I think that shift towards the darkness has a lot to do with that. I love the shades of grey in almost all of the main characters, and I love the friendship that has developed between Skulduggery and Valkyrie (that bit in the very end? the "Until the end" bit? I melt every time I read it, but then, I am a hopeless Val/Skul shipper, even though I fully expect that
to not happen in the books).