Meh. Brain damage isn't something to be underestimated, but I don't think this card is that good. For one, at two inf, I don't see much splashing outside of HB. Sure, this is one of the very few ice that punishes face checking, but you'll get early BP and one brain damage is easy to play around.
All I know is that when playing my naked Gabe deck, I won't think twice about the possibility of hitting a Fenris, because it's punishment is marginal. Katana is better in this regard, and has one additional str without the BP.
edit: Even OOF, it isn't great, as you need more than one copy to ensure you get it out early, spending 2 influence a pop. Honestly I hope to see plenty of Fenrir as a runner, either because it's influence not spent on Archer/SE/Overwriter, or because it's easy drip economy for me.