It would be great if we could, not only select the # of questions we wish to review, but also select from which card. For example, if I have an exam coming up and I want to select a few sources to study from, that would be really helpful.

Having features like how many cards do you want to practice daily, and being able to customize how often the cards are recalled would be great too.

Someone else mentioned streaks, and I think that is also a great way to track motivation.