It never did any child any harm to have something that was a tiny bit above them anyway, and I claim that anyone who can follow Doctor Who can follow absolutely anything.
Hee. Writing in 1992, so it was OldWho, too. And I just noticed when rereading Hexwood the other day that it's dedicated to Neil Gaiman.
One of the books she was specifically confronted about by a parent was Homeward Bounders, which *is* quite an adult and complex book. I read it when I was 10 or 11, I think. And re-read it constantly until I understood all of it. It's one of my favourite books of all time, and I think it's where I got my taste for somewhat unhappy endings from. (Note to RTD: When they're done WELL, that is.) It's interesting to note how many tropes that I still love are used in it, too.
Oh, the dianawynnejones community is reading Hexwood and discussing it. Ve-e-ery interesting, because it's a complicated as hell book.