Enchanted Glass is the next-to-last novel by Diana Wynne Jones and has a lovely, comfortable feel. It uses a lot of her recurring tropes--an orphan, a slightly-absent minded (but less so than he appears) professor, loyal-but-bossy staff, a smallish village with quirky characters, a bad guy who's intent on stealing as much magical power as possible and never mind the damage done to others, and the grinding horror of a certain type of mundane urban life.
But what made Jones such a wonderful writer is that she could take those same tropes and weave them into unique stories every time, with characters who are flawed but engaging, so that you want to spend time with them and see them succeed against the odds. In this case, she also adds in the new premise of "doubles"--or as we might call it, "good twin, bad twin", though the twins are magically, not biologically. Oh, and there's a weredog, did I mention that? He's a sweetheart.
If you've enjoyed other books by Diana Wynne Jones, you'll probably like this one too. If you've never read her works, well, this is just as good a place to start as any, and you really ought to try her out. I continue to enjoy her works now just as much as when I first read them as a kid, 20 years ago.