The technical level isn't that surprising IMHO, I think at least a few other gacha games also do decently well in that regard.This should be a given for a new game launch, but somehow it's such a rarity. It's either crashes, server being overwhelmed, co-op not working, constant disconnects, barebone content, or the combination of all that. Genshin Impact has none of that, it just works.
What makes Genshin Impact very surprising to me, at least so far, is how much the gameplay doesn't suck -- or semi-forcibly push you to spend money.
I'm still ready and waiting for that to happen though. (Which is why I'd genuinely enjoy the game even more if it was P2P; then I wouldn't be waiting for the gacha shoe to drop)