This game has one major selling point that I haven't seen anyone mention yet: It is full of attractive girls in revealing outfits. In addition to making the game more enjoyable, this pours rocket fuel onto distribution since it leads people to make fanart.

This is not a quirk of Genshin in particular, but a core feature of the genre, as evidenced by the huge number of gacha games on the app store that also have this feature. They may differ from Genshin in setting or core gameplay mechanics, but beautiful girls are a constant. People who play these games often say that it doesn't factor into their enjoyment ("I thought the story was unique, the endgame was engaging, etc"), but the download numbers say otherwise. Since my HN account is a pseudonym, I will readily admit that I considered getting into this genre, and my primary reason was the appearance of the girls in the promotional materials.

Unironically, I would consider this something of an innovation in game design. Western games never used this technique as openly as the gacha genre, and lately they have become even more conservative. As an example, compare League of Legends in its early days to the game today.

I think there is a huge opportunity in this space for any Western game company who borrows the wisdom of our Eastern counterparts.