"What is your favourite genre?"
This question is deceptively simple and open ended, but it's actually a very dangerous question to the untrained eye.  I'm still not sure whether my answer to this is ever correct, and I think that's the point, there's no "correct" way to answer this depending on the company and what they're looking for in a designer.  Let's look at the options and why it's dangerous:
1) My favourite genre is X - The obvious, straight forward one of answering truthfully, which sounds like a good answer, BUT possibly not a good one.  Does X align with what the company does?  If not, then why bring it up?  If you're favourite genre is racing games, and you're interviewing with a FPS studio, then how relevant is it?
2) I play what's popular with the general crowd - Shows that you're in tune with what's out there right now, BUT does it also show that you don't have a focus?  Do you as a designer even have your own opinions, or are you that easily swayed by other's point of view?
3) I play everything - No.  No one ever plays everything, and, this easily sets you up for a fall when the interviewer asks you for specifics to a genre/game that you may or may not have played.
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So yeah, I'm not sure exactly what a nice answer, or a good answer is.  How would you answer if you're in such an interview?