as for demakes, Halo 2600 is an achievement. It had an official blessing from Microsoft, and rather than try to make a first person shooter, it took elements of the Halo universe and reimagined them for the VCS. It also made mainstream headlines and got people interested in the 2600 that would otherwise have zero interest. As much as I hate to admit it, if your hobby is not growing, it is shrinking. Halo 2600 was a shot in the arm to the 2600 scene.
(even though it is not the best homebrew game out there, it is more than good enough to serve its purpose)