Genshin Impact is a free-to-play RPG that looks like a clone of Zelda: Breath of the Wild, but with a gacha-style progression system where you unlock new characters and loot from random drops. Despite those mobile game roots it has a huge open world, a fully voice-acted story, and the combat is pretty fun, too. It released just today on PC, mobile, and PS4 (with cross-save support between PC and mobile), but if you're trying to download it you might be running into some dismal download speeds.
Fortunately, there's a simple fix: try pausing the download via the launcher and resuming it. You won't lose any progress, but a lot of players are reporting that it significantly improved their speed—and it worked for me and another editor, too. I was stuck looking at a 10-hour download going at a miserable 0.3MB/s, but after pausing and resuming the download a few times I was able to get up to 1.7MB/s. That's still awful, but it shaved my download down to just two hours, which is much more tolerable.
If that doesn't work, you can also try exiting the launcher entirely and restarting it. Again, you won't lose any download progress, but there's a good chance you'll see slightly improved speeds. If you don't, keep trying to pause or exit the download a few more times. It seems completely random: Sometimes the download would be much worse, other times it'd pick up speed. Either way, Genshin Impact is only a 15GB download, so it won't take too long if you manage to get it higher than 1MB/s.
What's unclear, however, is what is causing such slow downloads in the first place. Genshin Impact is developed by MiHoYo, which is based in Shanghai. If the servers are also located there, that could explain it. Though the game feels like it came out of the blue, it's also possible that there's just too many people trying to download it right now and the servers are at capacity. Either way, give the above advice a shot and see if it helps. We'll update this story if we find more tips.