The game centers around the main character of Apollo (no relation to the Greek sun god) who progresses through the game in an alternating format that switches between platform, side-scrolling action (similar to the Super Mario Bros. series) and side-scrolling shooter action (similar to Konami's Gradius series). The goal of the series is, stereotypically, to destroy an evil boss — Goruza — rescue a princess — in this case, Princess Maria — and save the planet.
In the platforming levels, defeated enemies drop life ('L' blocks) or money ('E' blocks) powerups. Apollo collects the currency of the land ('Balls'/'E Ball') in order to exchange for acquiring power-ups and information, as well as access to minigames. Vendors are scattered throughout the platforming levels through doors or hidden gates. In the shooter levels, 'S' and 'P' oblongs are found that upgrade speed and weapons, respectively.
Source: Wikipedia, "http://www.wikipedia.com/Xexyz," available under the CC-BY-SA License.