Thanks for your question, it gives me the ability to nerd out on linguistics a little bit!
As mentioned, the hallmarks of a successful language learning curriculum are engagement and immersion. I misspoke when I said that "nothing does engagement and immersion better than video games." One thing does engagement and immersion better than video games: VR video games.
VR does other things better than video games too, and a million times better than textbooks. For one, VR excels at spatial conceptualization. This is important because one of the many obstacles Korean speakers face when learning English, believe it or don't, is spatial reasoning. Consider the following sentence:
The teacher is in front of the whiteboard.
In Korean, a literal (machine) translation looks like this:
Teacher whiteboard in front of is+polite participle.
If you parse this incorrectly you will focus on the "whiteboard in front," and in instances without contextualization, get the objects' spatial relationships completely backward.
Here we're working from English to Korean but believe me, the confusion goes both ways! Ask any native speaker teaching in Korea, prepositions wind up being the longest, most frustrating modules there are. Sadly, they don't understand Korean sentence structure and so they haven't a clue as to why. They simply repeat the book's lessons louder.
By standing my students up and having them orientate themselves according to prepositional imperatives, they were better able to understand the spatial relationships, and by extension, English. Again, this isn't something that can be accomplished in a book.
It can only be accomplished (mass produced) in VR.
Thanks again for your fantastic question johnsoncreek (let me know if my answers have/haven't been sufficient)!