So far so good: interesting and useful.
I like the succinct style. It didn't come off as imperious or authoritarian to me, merely brevitous. However, I did wonder if you might want one wordier and less succinct 'inspirational' paragraph near the beginning. A sort of, 'yes you can' paragraph. Sometimes the thing that stands in people's way isn't lack of skill or ideas, but a psychological block--questions about whether I can really pull this off?
I wondered if somewhere early on, maybe in the prologue, you might also want to include some brief notes on your views re: playtesting. It's an important part of the process and even if you don't discuss it in detail, sign-posting it early on might be good.
Otherwise I don't have any major comments except that I enjoyed reading this and it reminded me to focus on some elements of design that I'd let slip away from the front of my headspace lately.
Thanks!
Chris