If answering the question tells you what you want to know about a candidate, then it's a good interview question.  If it doesn't tell you that, it's a bad question.

Easy questions like FizzBuzz do serve a specific purpose.  If a candidate can't code FizzBuzz, they simply can't code and you can end the interview early.  I'd rate implementing a linked list only slightly harder, but it can start a conversation about data structures in general that will reveal a lot.

Just remember that no single interview question will tell you everything you want to know.  You really need to have a group of questions ready.  You should ask questions in a sequence from easiest to hardest so you can find the *limit* of what the candidate knows.  If you ask one question and they nail it, you still don't know what else they do or do not know.