Write what you like

Hello, gentle reader.  I hope that you're having a nice weekend.  Maybe sitting at home in the easy chair, reading this on your laptop.  I'm going to imagine you sitting there with a frosty beverage close to hand, because you deserve one.  I think it's been that kind of week, hasn't it?
Earlier, someone asked me, "Why do you write that weird stuff? Why don't you write something normal?"
My answer?  "I write what I like."
Which, I think, is one of the most important things that a writer can do.  Mainly, because if you don't write what you like, I think you'll rapidly lose interest in it.  Also because when we write what we like, I believe the quality of the work will be better than if you're writing something you don't honestly care about.
That said, maintaining interest in a long term project, like say a novel, can sometimes be a challenge. Which is why I'm one of those writers who tends to keep a couple of projects going at one time.
Creative fatigue is quite normal for people, so I think it can help a lot to shift gears. 
If, in that mystery you're writing, you've reached a point where the idea of massacring all your characters is suddenly very appealing because you just can't take it anymore, then it's probably a good idea to switch to something else for a day or so.  Maybe that Regency romance you've had tucked away in your desk, or the latest chapter in the epic fantasy you've been working on since middle school. Then, when your murderous impulse has subsided, you can return to your mystery and not have to worry about impaling your detective on a falling cast-iron weathercock.
Or, if you have to, write that scene.  Massacre the cast.  Have the enormous wrought-iron and crystal chandelier collapse on them at the dinner table.  Have the cook poison them. 
Who knows? Maybe you'll like what you write even better and your mystery could turn into something else?  Perhaps the first chapter in a zombie apocalypse story?  Murder on the Orient Express meets Night of the Living Dead.  Who knows?  It might even be a smash hit and make you millions.
But you'll never know, gentle reader, if you don't write what you like.