The Merchant Princes series is fun, and I really enjoy the story of why he wrote it. It starts out as fantasy for basically the whole first novel and then some. But you can find some evidence from the start that it's really sci-fi, and by the end of the series it has dropped all pretense. It's sci-fi through and through.

This is all because he had an exclusive contract for sci-fi with his other publisher. But not an exclusive contract period. So he stealth wrote a second sci-fi series without actually breaking that contract until later.

I'm not sure if The Laundry Files was done for the same reason. It's possible. I haven't read those past the first novel. But I'm a big fan of everything else he's done.