Something I notice is that a lot of famous(-ish) authors I read like to play with genre boundaries:
- Arthur Conan Doyle. Every Sherlock Holmes novel feels like it's playing with genre boundaries in some way.
- Brandon Sanderson. Mistborn is a fantasy story that's also a heist story.
- Stephen King. The Gunslinger is such a wild mashup of different genres that I don't even know what to do with it.
- Terry Pratchett. The Discworld forms a base world of comedic fantasy — yet for example Night Watch is also a "manhunt" story and works on that level too. The funny bits don't detract from the serious bits. The fantasy element is not only a source of jokes.
- Dan Simmons. Hyperion is a lot of genres or tones mashed up together.
On a related note, although he's not famous (yet?), John McCrae did this a god amount in Worm.