Ion Assault is a twin-stick shooter involving a spaceship in enclosed space arenas akin to Geometry Wars. The left stick controls movement, while the proper one controls targeting, as shown by a red laser. The goal is to survive waves of adversaries and space debris (mostly boulders that break down into more minor elements akin to asteroids), but there is a twist. Instead of shooting directly, the ship can engage a mass reactor, which slows movement but allows the boat to amass a vast amount of ions floating in the arena and concentrate it around the ship. The amount defines the damage, which is shot in the chosen direction. These ions ricochet off walls and can thus target several foes or be caught before spreading out again in the playfield. Because there are no other primary means of attack, the “bullets” are scattered around the field, waiting to be gathered and recycled.
There are four primary levels with five stages each and a boss fight. Ships that are destroyed leave behind score orbs that can be collected. Certain ships carry power-ups, which are classified as active or passive. Gravity power-ups, for example, increase the range of the mass reactor, whereas a shield momentarily protects the spacecraft from hostile attacks. There includes a suitable option as well as multiplayer throughout the campaign. The gameplay in the latter is radically different, as the player must summon friendly ships to target the opponents and vice versa.
