The game has changed 3 different engines during its development and i am sure it would still be on a outdated engine. The trailer which came out about a year back looked dated(gfx wise) almost proves that and i am sure that 3D Realms will have a real hard time cause about 2 years back they were in a situation that they had to release this game otherwise the company would go bankrupt and it will not be a shock that even after releasing they release the game they would still need to shut doors of their offices.