This game is almost too good.
Less than an hour into the game, it's very clear how well-designed GS is and how much of a slog Pokemon SM's first hour is. Keep in mind that I love SM and it was my GotY last year... but GS's first moments really show a stark contrast between classic and modern Pokemon games.
Sun and Moon starts off with so many cutscenes and when you finally get your Pokemon after about twenty minutes, you have the advantage and then you're unleashed on a fairly standard Route 1. GS goes through the general tutorial stuff, but in a much quicker and more interesting way. There are so many teases of secrets and optional paths you can take. The first route, Route 29, has some trees that need Cut, hinting that the player should revisit routes to find more secrets. Cherrygrove also has a trainer that is inaccessible unless you have Surf, another hint that players should backtrack. Two completely optional areas, the southern tip of Route 46 and Dark Cave, have unique Pokemon you wouldn't find if you just followed the story route. Not to mention, depending on the time of day, your Pokemon team could be very different. Depending on your game version, you could encounter Pidgey, Hoothoot, Rattata, Sentret, Weedle, Caterpie, Zubat, Jigglypuff, Geodude, Spinarak, Spearow, Ledyba, and Dunsparce all around the first tutorial town. There's even more in Crystal. Early on you are encouraged to satiate your own curiosity.