Hexen II: Continent of Blackmarsh is an extremely rare demo version of the game that was bundled with Matrox M3D series video cards. It includes the entire first chapter of the game.
As the included opengl32.dll is a 3dfx-specific MiniGL wrapper, it should be deleted on systems not using 3dfx cards.
This is one of the few games that have problems with long OpenGL extension strings. Regarding Nvidia, older drivers had the option to toggle extension string limit, but current drivers omit this option and instead have all problematic games hardcoded to limit the string. Therefore, the game should start up fine with up-to-date drivers. This can be verified and altered via Nvidia Inspector.
XP SP3 compatibility mode fixes this issue.
This is a type of copy-protection, activates if you reinstalled the OS or moved the game to a different computer.
You can reinstall the game from the CD, install Hammer of Thyrion, or ensure that you also copy registry key HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\ComputerName\ComputerName\RAID.
FixClamp = 0
FixClamp = 1