I've never really played any mobile games other than Pokemon Go, a Minecraft clone, and some weird city builder thing so can't really comment on that. 😅
For me, it feels like an ARPG but out in a mass multiplayer world. I love that I can solo all the things I need to, or join a group if I want to. Especially dungeons. And especially because there are collectibles hiding in those dungeons, being able to slowly hunt them out at my own pace is wonderful to me. Have already backtracked through the first three and found some wine that's apparently for cooking later on and some of those mokoko seeds.
I think it's because there is so much to do in the game. Gathering, crafting, ship-building, island exploring, treasure hunting, archaeology, collectibles, etc, for people like me, and pvp, a lot of bosses, being the best of the best, for the hardcore people. From what I was reading on Reddit a while back, apparently it's a lot like PoE in that the game doesn't really start until you hit the end of the story. So... we'll see!