I'll try to make this simple:
1. Its free fantasy anime styled game
2. It has a great main story
3. Visually is stunning
4. Open world is huge, and I mean huge (and diverse)
5. Combat is good enough, it requires some practice and knowledge of reactions
6. Number of playable characters is over the top, something for everyone
7. If you want a fast paced game, this is not for you, if you are in for characters and want them all; it will cost you real money, but it is really not necessary, game gives you for free everything you need to play it and experience everything that it has to offer, rest are cosmetics hidden behind gacha system, nothing more
8. Even that "evil" gacha in this game is kind a ok, by playing the game you will for sure earn and get few more characters and weapons without paying anything, or let me put it this way: F2P is really good in this game, F2P friendly
9. The game it self is in constant development, expanding world, new stories, new things are coming every month, so there is always something new to do, see, find, get,..
10. There are some repetitive things in it, like grinding for experience and materials, but its rewarding, its like, they gave you this beautiful world for free and now you must earn your way to stay there, how is that a bad thing?
11. Did I mention its free?? For all that complains about gacha cosmetics and their rant how its not fair; why would anyone do anything this good for free??! Did devs hid anything from ones that are not paying? No, so let me repeat once more: its free and you actually dont need anything, but if you want something like a spoiled child and rant like: why they dont give it for free, its not their fault, its yours!
12. I played games since 80's, so many titles, so many types of games, thousands, thrust me, please, when I say: there are only few game titles that are memorable: Genshin Impact is one of them...