It is easier to have alien life in both a novel (descriptive) and a comic (visual) than in a video game (kinematic).
Want a cast of thousands? No problem. Need a mob of hundreds of individuals representing fifteen different species rendered inside an colossal ancient space station? No sweat.
Clearly this person has never made a video game.
I don’t need to explain why the option to have a non-white, non-male, non-straight person as the main character of a blockbuster action science fiction story is important.
But you do need to be explained the difference between shared and tailored culture. Having a "diverse" hero of a popular television show has an affect on society. Having a "diverse" hero of the instance of the video game that you are playing has an affect on a single individual (and maybe some friends).
One can spend hours tweaking physical appearance (not mere a few options of “races”) to get a character of any ethnicity and build. Oh, and sexuality is an option too. Shepard is yours to design.
That's just windowdressing the choose your own adventure. The backstory that you change won't affect the plot any more than picking a "race" in those "unimpressive old games".
I opened this hoping for something insightful, but was presented with an adolescent boy's wonder of a story written in a shiny medium. For all of the alien diversity, every picture on the page is humanoid. For all of the glory of the malleable video game, a descent novel would have twice the depth and ten times the perceived diversity. He purports to appreciate the humility of the portrayal of humanity, but it sounds like the whole story is about a rise to power.
If you like Mass Effect this much, do yourself a favor and go read a good book.