The mecha, called Overkill Engines (OKEs), cannot be directly controlled in battle; their actions must be planned beforehand with effective tactical planning, programming and resource management, making it unique from other mecha games for its more strategic approach.

[2] The game features a fairly complex negotiation system that allows the player to purchase, research, or upgrade new equipment and parts.

After a body has been selected the player then must choose a main weapon, sub-weapon, engine, CPU, fuel tank size, armor thickness, and any optional equipment.

Thick armor is very heavy and usually only found on the tank types, since they are very efficient at using engine power to haul mass, while the flying type OKE will require powerful engines just to fly with the thinnest armor in the game.

Instead the player is given a board, which varies in size depending on the CPU selected during the hardware design phase, on which to place chips to act as a set of instructions.

Each chip that is available to the player performs a specific task, and many can be edited to allow more precise control over actions.

Actions include simple movements, aim and fire operations, scan for enemy or friendly units, incoming projectile detection, random number generators (to give, for example, a 50% chance of jumping left), variable assignments and checks, and even rudimentary inter-OKE communications, affected by assigning a color to a "channel" which can then be read by other friendly units.

The mission is always to simply capture each enemy base on the map, and it becomes increasingly difficult as the game progresses.

[6] Reviewers generally commented that its gameplay is deep, sophisticated, and well-implemented, while warning that most gamers would find its complexity overwhelming and the lack of direct control over the mecha frustrating.

"[11] GameSpot assessed it more moderately, but still positively: "For those who don't mind building a mech from the ground up, determining its every action, then relinquishing control of it when it gets on the battlefield, Carnage Heart will surely provide long hours of highly-detailed futuristic military strategy.