Depends.

I happen to enjoy riddles and am happy whenever one actually has real life application. Others only like real life problems. Which might make teaching a bit more complicated.

A big problem I see is when important problems are ignored because they are not particulary interesting or worse stigmatized. Norman Borlaugh probably did not enjoy his research too much, but it was necessary. A related problem would be when especially gifted people end up in one field of research, and not in another on a systematic basis.