A remake or remix of the first episode in a series (usually a video game series) which usually creates many new interpretations of the old elements, dramatically adds depth to the plot, and employs quality, technique, and style which evolved since, but were not present in, the first episode.
Most of today’s popular video game series were first developed for archaic video game systems such as the Commodore 64 or the NES, which didn’t look all that great compared to today’s technology. Because of this, if you go back to play the first game in any given series, you will probably find simple and unimpressive (and sometimes poorly-made) graphics, controls, level design, and music. A good plot was also hard to find back then, often only existing in the instruction manual which accompanied the game.
As technology improved, many of the games developed sequels and turned into series. These sequels built upon their predecessors, employing an increasingly more impressive style and technique with each new release. As each series became more and more fleshed out, similarities to their premiere games became more and more unrecognizable.
Zero Missions are an increasingly popular fad in video game development today. The idea behind a Zero Mission is to revisit the basic premise of the premiere game, this time in drastically better style of the game’s sequels. A Zero Mission will almost always employ similar level design (not identical level design, but design full of obvious references), remixed music, and improved graphics to its predecessor. Also, storyline and plot aspects (especially aspects which were introduced into the series after the premiere game) are usually executed and explained more clearly than the first time around.
A Zero Mission is not simply a port with improved graphics, it adds just as much to the series as the other sequels have.
Metroid Zero Mission, a remake of the famous classic Metroid for the NES, seemed to start the growing fad of remaking games in the style of their sequels.