I was a little surprised to not find too many sources on this one while googling around. I realize there are probably a couple of essays that I missed, but you'd think something like explaining how your game works to a total stranger would be a pretty refined concept amongst game developers. If Nintendo got ahead by bucking the trend and making games easier to play, it stands to reason this revolves around the game being conceptually easier to understand. Wii Sports for bowling is just "Press B to swing, let go of B to let go of the ball." The tutorial is literally just two sentences. So presuming you're selling a much more complicated and nuanced game, it's pretty obvious you need to make sure your tutorial is engaging and fun to work through.
Which makes the bizarre array of tutorials out there a little puzzling. You have everything from GRAW's lengthy lecture series, Fallout 3's slow growth process, to Persona 4's noxious inability to shut up and let you play.
It's a diverse topic and there are numerous games I didn't include. I picked examples of two open world games (Fallout 3 and Far Cry 2) and contrast their tutorials. I also take a game like Beyond Good & Evil whose tutorial works by mostly being self-evident. Then I just kinda rattle off a bunch of other conceptual examples.
The point being, the first 15 minutes of a game are probably the most important.
Bonus: you can start to see the stress of exams getting to me as my grammatical errors start to increase.