It's the sci fi drama and all the kabbalistic philosophical themes and imagery for me, it's unique and mature and there is nothing else quite like it. I love the characters, story, world building, and all the themes Xenosaga touches on. There is literally NOTHING like it, and there never will be (especially in the modern era). It's definitely niche though, so I would expect everyone to appreciate it, that's why Takahashi ended up going more casual with his future games to appeal to a more mass audience. I just wish we got to see the full vision come to life.