fyi that game uses steamworks so you'll need to activate it on steam.
I just bought it, since I always wanted to try that game, and it's a good price, but it's the first time I'm buying from GamersGate. It indeed has a key that can be copy-pasted to register it on Steam (which I've done myself just minutes ago), but it's not showing immediately after the purchase. I just want to warn others around about that.
To show the key itself you'll have to open the "My Library" tab on the left (if you're logged-in to your GamersGate account obviously) and then under "My Games" should be shown the games you've purchased. You click Darksiders, and to the right side of the page you'll see the title "Darksiders" under which are five white stars, and under that are some options and the game's retail box picture... and under that you should see a button that will reveal the key if you left-click on it, and then the key will be permanently shown there at all times.
Hope it helps. And as a side note thanks for the heads up about the good price on it, I wouldn't have bought it otherwise (nor would I have been aware of it, GamersGate is a no name seller to me as of now but so far so good, nice site, everything is straightforward, fast and simple).
Facebook
Twitter