Nobody seems to have picked up on the point that the game engine is pretty awesome... So mods, etc. developed for it will hopefully be Linux friendly... The lighting model looks pretty decent to me (from looking at the demo videos). Linux desperately needs some decent native proprietary game engines...
As for all the stupid comments about not sinking money into a black hole... The devs. have weekly Youtube channel you can subscribe to. What more do you want??
@bobwya, The guys behind OilRush developed UniEngine, which you probably know since you're on Phoronix.
@bulletxt, Lugaru was purly a bunny combat system. I am sure Overgrowth will follow this, but with improved mechanics and multiplayer. I wouldn't expect much more. I was skeptical at first, but having played Lugaru, I know it works.
Kind of wish Overgrowth engine => Oni 2... Bungie? But I don't actually want a sequal, I'd just want of the same style.