Alienation is a twin-stick shooter with a fixed perspective. While there are some cutscenes and radio messages during gameplay, the story (aliens have conquered Earth and the player has to defeat them) does not play a major role: the main occupation is walking through the levels (overall 20 in various environments such as Alaska, Brazil or Russia) and shooting everything which moves.
The controls follow the usual formula: one stick is used for movement and the other for aiming (independent from the movement direction). Additionally the player character can use melee attacks, grenades or special abilities with a cooldown period. The latter are dependent on the chosen class: Bio-Specialist (healing and area of effect damage), Tank (protection and splash damage) or Saboteur (scouting, melee and air strikes). Overall each class has four active and three passive abilities which are upgraded after level-ups, The level cap is 30, but afterwards the character earns hero levels which improves health only.
Defeated enemies leave behind many weapons the player can collect. Those come in five quality ranges (from standard to legendary) which influences their statistics (damage, speed, magazine size and critical change). It is possible to use resources (mostly gained by dismantling unused weapons) to improve one statistic. However, the result is random, but becomes more favorable the more resources are applied. There are also power cores to find which can be mounted into weapons. Besides killing enemies and searching containers, a third way to receive rewards is finishing a level. The reward improves when destroying checkpoints (after death, the character respawns here) instead of activating them.