Well, you get 2 cdkeys on steam anyway, which i've applied on my Trion account (where my Rift stuff is) and it works nicely in there. So i'm not even sure whether you have to download via steam or even play via steam. I'll most likely try download directly from Trion, since my trion account now reflects i have bought the game. Steam is notorious for being pretty bad with MMO game clients which are updated outside of steam.
Anyway, on a side note, for those that is purchasing or at least have a Trion account, there's these Arkfall Codes that were supposedly hidden in all the PR material , these codes can be entered here : http://www.defiance.com/en/my-ego/ and it gives all kinds of in-game rewards/items . Now luckily for us, there's a site with almost all the codes:
http://orcz.com/Defiance:_Arkfall_Codes
Oh and the TV Series Trailer, just to give a background for the game:





