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please move these files to separate folder somewhere:

setup_darksiders_2.0.0.6.exe
setup_darksiders_2.0.0.6-1.bin
setup_darksiders_2.0.0.6-2.bin
setup_darksiders_2.0.0.6-3.bin

and afterwards run .exe file only. This should start the installation process.
What happens when you double-click the setup_darksiders_2.0.0.6.exe file?
Edit: Ninja'd. As expected.

We strongly advise using GOG Galaxy - our new application which makes downloading and installing games as convenient as possible.
Besides being very user-convenient, and keeping your games up to date, it offers the fastest download speeds possible, pausing/resuming, and - most importantly - thorough protection against file corruption while downloading.

Just click on "TRY GALAXY", then "DOWNLOAD BETA" and install it on your system. Afterwards, just launch it, log in, and you can install games directly from your Library section.

If you just want to download the installers, please find the game in Galaxy, and click MORE -> DOWNLOAD EXTRAS. This will let you download the installer, which you can back up and/or install at any time.
Post edited May 15, 2015 by Firek