Maybe it's cause I played Panzer Dragoon 2 first, cause I really don't see the likeability of the first game.
It's clunky, sparatic, and just down right boring. The second one has a much better pace varying between ground, and air assault, and just a better interface all around. It's a much higher quality game, imo!
Was the first one ever that popular, cause I don't really know the history of Panzer Dragoon, but I wouldn't think it got popular till the second one myself.