Continuing with his coverage of Game Center CX, Chris Kohler has posted descriptions of the game's progression, along with details about each of the games. A few games at a time are unlocked, and you earn more games by completing specific challenges. For example, getting all your characters to level 7 in the Dragon Quest-like Guadia Quest, or shooting a giant asteroid in the Galaga-inspired Cosmic Gate fulfill requirements set by the game.
Every element of Game Center CX accurately parodies Japanese retrogaming: Rally King SP is a remade version of the (also fake) top-down racer Rally King with branding from a fictional ramen company. Product tie-in games like this were common in Japan at the time (though they've all become frustratingly rare now!) and in fact, some, like Gradius: ArchiMENdes Edition, were actually given away by ramen companies.
The "challenge" focus of the game actually sort of makes Game Center CX a bit more modern. Rather than simply completing levels, you're fulfilling objectives. It's almost mission-based, but in an interesting way.