The two sides of the valley are style and photo-realism. Unfortunately, in games, we've yet to achieve true photo-realism and this makes the flaws much more glaring. Having stylised games opens the game up to more artistic variety but still has some pitfalls. The video explains it much better.
How might this affect my MA? I much prefer exploring styles in games but that's not to say I don't like photo-realistic games. I find it much more fun and appealing exploring styles and themes artistically. After coming to the conclusion that aesthetics alone don't affect immersion in games, I think it'd be beneficial for me to focus on style exploration.