Literature review on adaptive game-based learning

I need an academic literature review of 2000 to 3000-words regarding the following question:
"How is adaptivity applied in game-based learning and what determines its effectiveness?"
Adaptivity is the adaptation or changing of the game environment in response to the players' actions. I am specifically interested in game-based learning for adults/higher education. However, I fear the literature may be scarce when limited to this group.
The work must be plagiarism-free and copy-edited. The reference style is APA. The review should include a full reference list.