One problem I've seen is that most addictive things, including games, either offer a diversity and discovery of content (as seen in watching YouTube videos or playing incremental games), or foster competition and demonstration of skills (as seen in games like chess or FPS). However, memorization is by nature a repetitive and solitary task.

Duolingo operates in this space, and their gamification model, I believe, is to motivate users to study by allowing them to display their streaks and levels to others. (competition)

Anki also has a streak-based gamification, and it's somewhat successful, as seen here: https://www.reddit.com/r/Anki/search/?q=streak&restrict_sr=1.

However, these gamifications are not as fun as real games. It won't make your heart thump like FPS games do.