I have to admit I'm actually glad this series is going to be over next year, with just one book left to go. It's been a fun, exciting, awesome ride - but it's definitely time for it to be over soon.
I've been complaining about the formulaic-ness of these books for a while now, I think, and this was really no exception. The quest-based formula in itself doesn't really lend itself to a lot of change, it seems - sure, it's exciting and all that (although I admit I struggled with the first half of this one; it was rather slow going not because of the plot, but because I found it hard to stay engaged and to care), but the basic story is the same.
Every. Single. Time.
Demigods have to do stuff, demigods go out on a quest, meet some monsters, kill some monsters, are in life-threatening situations, kill some more monsters, finish the quest more or less victoriously but the victory never means it's all over - nope, they have to start all over again.
This is the formula. It works, because, as I said, it's a formula that allows for an exciting, fast-paced, entertaining adventure. It's just that after nine books, I find it harder and harder to stay engaged - the feeling of deja vu is stronger with every book.
All that said, The House of Hades was by no means a bad book - not at all.
At some point I actually finally got into the story again and then it was interesting and everything I could wish for in this series. There was even some much-needed character development - personal growth and maturing for all of them. Hazel, somewhat to my surprise, probably ended up my favourite in this particular book, and Nico... well, I'm in two minds about Nico. On the one hand, the revelations we got in this book made sense (and for a lot of reasons I'm happy Riordan made those choices); on the other hand, I'm not sure I care for the sense I got post-revelations that all his mysterious brooding don't-touch-me lonerness was just due to, well, That Thing. I'm hoping I was wrong about that and it's just the way it came off to me, really, because I really like Nico and I'd rather he had his own reasons to be the way he is.
Anyway. I am looking forward to the last book, although I suspect it won't all have an entirely happy ending - there'll probably be death and stuff. Fortunately for me I'm not really invested in any of the characters sufficiently to be heartbroken by it. Heh.