In Digital Games, Complexity Matters Marc Prensky.com
How do we bring to learning the intense concentration and commitment students give to their video games at home? Marc Prensky takes on this subject in a number of his writings. In particular this paper (published in Educational Technology) looks at the differences between simple games that we often see and the complex games delivered via Nintendo, etc.
There's nothing really deep here; see the recommended books for more. But it does serve as a warning that making a lesson an online game does not necessarily make it more engaging.