Transformers: Devastation is an action game based on the Transformers franchise, specifically the original cartoon series from the 1980s now known as Generation 1. It has the same bright visual style using cel-shaded graphics. The main story mode has five difficulty levels and tells how the Decepticons plan to cyberform planet Earth after Megatron finds a way to control plasma energy. He uses this technique to turn organic material into metal. The Autobots need to prevent this and eventually five different characters are playable: Bumblebee, Grimlock, Optimus Prime, Sideswipe and Wheeljack. Next to the main story mode there is a challenge mode.

The gameplay is similar to other titles by developer Platinum Games. The game is largely played as a 3D action brawler where missions are divided into smaller areas with short cut-scenes in between to further the story. The Autobots link light and heavy attack in different patterns to form combos. When a blue flash appears during a combo it can be finished off with an attack in vehicle form. Robots can freely switch between robot and vehicle form. The latter is used to move around quickly and there are also longer driving sequences, often when chasing or escaping. While driving, ranged weapons can be fired and there is a rush attack and often obstacles to dodge and booster portals to receive extra speed. Melee weapons include swords, gauntlets and hammers and ranged weapons are blasters, grenade launchers etc.

While fighting in robot form, four weapon slots are available per character. A large amount of melee and ranged weapons can be collected during missions and they can be switched on the fly. Ranged weapons have an energy meter and when empty require some time to recharge. Another meter is filled up by attacking and when full a devastating attack can be triggered, unique for each Autobot. Levels often have hidden items and collectibles. There are transpatial converters that temporary reveal a hidden container in another location. A stomp attack launched from the air is sometimes used to reveal items hidden below the surface. The Autobots can also pick up and throw objects and this technique is sometimes used to solve small environment puzzles. By timing correctly incoming attacks can be dodged, which slows down time, similar to Witch Time in Bayonetta, providing an opportunity to counter. Additional attacks can be purchased later on, such as a parry move where an incoming attack can be countered right away. The game has many encounters with large robot bosses where weak points need to be exploited. After each fight a ranking is shown based on the performance.

During gameplay green and blue energon cubes can be picked up to restore health and weapon energy respectively. New missions are always started at the Ark headquarters. The player gets to select the Autobot and can define the loadout from the large inventory of weapons. Weapons have their own levels and can be made stronger through synthesis, merging weapons with a base one and the secondary ones used for parts. The credits currency earned during missions can be given to Wheeljack. He develops T.E.C.H. that provides enhanced abilities. Players need to complete a quick timing mini-game to develop them and when finished they can be selected from a large pool for two slots. Equipped T.E.C.H. can be different for each mission.