You may run into an issue with the HUD going off the screen if you’re playing in 16:9, you can fix it by:
1: Open …\Dark Sector\Configs\DS.cfg in notepad
2: Put the following line under the [Windows_Config,/Types/Config] Graphics.DisplayAspectRatio=FullScreen4x3
and Save.
https://steamcommunity.com/app/29900/discussions/0/540734255021920399/
I think this might be related to the warframe ARG, they added some text to the steam listing saying:
Less related, but Unreal Tournament and Unreal Gold are also free. https://dormi.zone/post/3413855