Not sure how I missed this but Darksiders II and the season pass is on sale everywhere including GameFly / GameFly UK. Use the coupon code DOWNLOAD to save an extra 20% off your order and you get the best current price on both.
Darksiders II = $13.59
Darksiders II Season Pass = $5.43
Both require Steamworks.
Note that the GameFly site is down for maintenance currently, so I did the calculations with the Windows calculator. Prices might vary ever so slightly.