I've always thought this game was what Novotrade was trying to accomplish with Cyborg Justice(only with giant mechs, instead of humanoid robots) on the Genesis, finally realized by Capcom. Only to find that CJ is a year older, and was published by Capcom in the U.S.(if GameFAQ's is to be trusted on this one), in spite of Capcom not really appearing anywhere on that game's case, or title screens.
Button 1: Attack/pick up items
Button 2: Jump
Button 3: Shoulder weapon
You have 4 mechs to choose from, despite it only being 3 players max.
Every arm/leg/shoulder weapon has it's own unique attacks. If you should catch an enemy with the shock arm(hold 1 down as you attack), you can push them out if close, or pull them in if further away, and extend the damage to other enemies they might touch. With the default Arm, pressing 1, when extremely close, grabs enemies. Usually you have a better chance to grab them when moving. During this arm's grab, 1 strikes up to 3 times, Left/Right & 1 throws, and 2, 1 jumps and throws. Another arm extends and grabs enemies just by attacking normally. During this arm's grab, 1 will slam enemies into the ground(can be done multiple times, as well as hit multiple enemies), and away & 1 will slam enemies behind the player(same advantages). Every Arm has a 1, then forward quickly attack(the grab arm extends itself further, and the shock arm can charge this attack for something more powerful, and can even shield yourself for a bit, before the character automatically attacks). The drill arm has a lunge attack if you hold Left/Right before you press 1. The laser arm has a 1, then Up quickly attack. The shield arm has something different for all 4 directions quickly after pressing 1(Left guards for as long as you hold 1). 2, 1 jump attacks(in some cases 2 alone is the jump attack), and 2, Down & 1 dive attacks(some cases, just 2, 1). Both attacks depend on which legs you're using. Double tap Left/Right to run. Press 1 while running to attack. This attack also depends on the legs you're using. 1 & 2 simultaneously is a desperation attack. 2 & 3 simultaneously is a more powerful, more health risking, desperation attack.
Certain defeated enemies will leave behind unique parts that you can add onto your mech to replace other parts(you'll notice these parts on the enemies that drop them). These, along with health restoration items, and radio's, are the only items you need to manually pick up. Others can just be walked over. I believe the way this works is, in 2 or 3 player mode, you need to pick up a radio before a boss battle, and just before fighting the boss, an even larger mech will be dropped, that your mechs will attach to, which I guess is called Powered Gear, which explains the Japanese title. From there, any player can control the combined mech, until they're forced to separate.
Sometimes you'll come across enemy soldiers on the field that aren't piloting anything, and can just run them down. Similar sized hostages can be rescued as if you were picking up were items.
In bonus stages, you have infinite ammo, and can fire with any button.
There's really not much more to say. It was a unique concept in Cyborg Justice, and it remains a unique concept here, especially with the Powered Gear transformations in multiplayer mode.