I have been using ridiculously challenging (and interesting) chemistry questions for my 1st year chemistry class. To the extent that I have made the questions harder and had students focus on deep practice (as opposed to grades), I have found that students enjoy the quizzes more. Here is the quiz for today.
After such a quiz, I have students compare their work with a solution key. They then identify areas where they can push themselves further. Here is a questionnaire they complete.
The goal is that they will be able to write their own gnarly, challenging problem sets and solution key. Here is a questionnaire that guides them through that process.
I hope that students in my course define their own interests and objectives, and as they write their own interesting questions for their peers, they will render me obsolete.