The storyline is revealed through onscreen text, instead of animated sequences. Iron Man and X-O Manowar must team up in order to stop a team of supervillains from grabbing the lost fragments of the Cosmic Cube.
Both Iron Man and X-O Manowar can jump, punch, shoot an unlimited supply of laser beams (that can be upgraded through icons) and use a limited supply of fuel to fly. At the start of each mission, a computer screen informs you of your objectives.
During the game the player can collect medical icons to restore their health, and other icons to give more fuel, stronger laser blasts and a special icon that allows one mega blast from a character's armor chestplate. The game also allows one to destroy various gas canisters, metal wiring and control panels to locate more icons, deactivate certain weapons, or advance in the game.
Source: Wikipedia, "Iron Man / X-O Manowar in Heavy Metal", available under the CC-BY-SA License.