I thought this book by Cornelia Funke was amazingly written. I was blown away by the enchanting descriptions and fell in love with the characters immediately.
I personally think this series is better than Harry Potter, and if you or your children are worried that Harry Potter was Satanish or demonic, you needn't worry at ALL about Inkspell. The only major magic I recall is reading things and people into or out of books.
Language wasn't really an issue to me; the only two dirty words used weren't overwhelmingly offensive, and they tend to appear in most young adult books.
There wasn't anything blasphemous or anti-religious, and the only thing that might bother you are the White Women, or ghosts, that frequently haunt people terminally ill or fatally wounded ... it was, in my opinion, harmless.
If you are bothered by wounds or blood, etc., you might not enjoy Inkspell. A character gets shot, but survives, a couple of people get run through with a blade, and there is one brief battle in which quite a few folks die. Ms. Funke doesn't go into unnecessary or brutal description, though.
Now for some positive points in the book. In one part a character gives their life for another, which was an extremely loving and selfless act (quite emotional, too.) I think that Inkspell is appropriate for anyone over eight years old, though some of the younger children might get slightly bored or confused. I am thirteen and I adored it, so if you like fiction/fantasy novels you will most likely enjoy it also. It's not like epic fantasy or anything, but it delves very deeply into the realms of character and plot. Inkspell's main idea was basically good versus evil, and there is a clear definition between the two. In this book, good is good and evil is evil. It doesn't praise murder, deceit, etc., in any way. There was no adult content, if you take my meaning, whatsoever.
Overall it was a wonderful and exciting novel, and it ended far too quickly!