It’s a great design. It’s a great card of course, but ultimately it’s also very expensive for a piece of ICE that lets the runner bounce of safely and that is not overly taxing. It’s also a poor card to put on remotes and does not prevent important runs from getting in.
It also suffers from Caprice syndrome. Yeah, it’s good defense but the Runner can just go somewhere else. And, unlike Caprice, it’s not that difficult to make that one, important run (Say, Legwork) through it. It’s unlike for you to cover all your centrals with it nor is it that great of an idea to stack them (because they’ll just run elsewhere).
Loki is unique because it has no type, like Mother Goddess. It may also be unique to prevent weird rules interactions, since it copies other cards.