Xenogears is easily in my top 10 favorite games of all time. I also enjoy Xenosaga and Xenoblade as well which are spinoffs of this series (and involved most of the same staff). Xenogears was revolutionary for its time because of the extremely dark storyline and incredibly strong religious overtones which were considered to be almost “too mature” for a video game, especially in North America.
It had both scifi and fantasy elements; by that I mean, it really went into depth in some areas explaining the scientific theories and concepts behind certain things – but then other things have a more “magical” feeling that require suspension of belief. It also blended high tech (mecha, A.I., and space travel) with primitive “fantasy” style settings and characters.