66% off on Steam for the next couple of days:
http://store.steampowered.com/app/107410/Arma_3/
recoil just got it and dan and I already have it, so that makes three of us. We are definitely playing it at some point, perhaps even before Ark if it's less demanding in terms of player numbers (I am not sure if it qualifies as an MMO, which is why I didn't mention it in the MMO thread), so get it if you can afford it right now.
The Apex expansion is also on sale and includes a new 4P co-op campaign and lots of other stuff:
http://store.steampowered.com/app/395180/Arma_3_Apex/
ARMA III - Launch Trailer
https://www.youtube.com/watch?v=Jioo5uXoNLg
Arma 3 Apex - Launch Trailer
https://www.youtube.com/watch?v=EwAxJC9AR_A