Have a look at the video on this page.
The low-quality video doesn't do justice to the skills of those guys. And the BF2 engine is no Plasma. It is more oriented towards fast-paced action than beautiful renders.
What they have done is known in the FPS games world as a "full mod", which completely changes every aspect of the game (visuals, sounds, music, maps, weapons, logic, avatars, gameplay, etc).
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