The one description summary is extremely straightfoward: destroy everything. Accomplishing that goal is another matter as Armored Core games traditionally have one the most complex controls in any game, and AC4 is no different. Every single button on the controller is used as you pilot your mech and destroy enemies.
AC4 emphasizes speed, evasion and maneuverability over power and defense. There are three different buttons meant for different kinds of boosting which propel your Mech in a specific direction at a greatly increased speed.
Customization plays a very large role in the game. Every single part can be swapped out and combined with other parts, and with dozens of part categories and each category containing a dozen optional parts, the possibilities are huge. Through customization players can create a Mech that suits their particular play style, and specific situation. Balance between different Mech configurations is achieved through a very deep stat tracking system that measures and calculates dozens of specifications of how the Mech performs, from top speed, to weight, to energy capacity, with each part affecting one or more of these stats.
Completing missions in the story mode, or defeating foes in the simulator mode earn you credits which can then be used to purchase new Mech parts.
There are three main game modes that involve taking your Mech and battling enemies. The singleplayer story mode is comprised of 5 chapters, with each chapter featuring between 1 and 10 missions, for a total over 30. These levels are all mission based and revolve around destroying targets, or protecting an ally.
The simulator is a mode which lets you battle a computer controlled enemy Mech in a one-versus-one arena. After defeating the Mech you gain access to their schematics and AC money to be used for purchasing new parts.
Online, the first for Armored Core, pits human controlled Mechs against one another. Battles can be from one-on-one up to 8 players in battle royale, or team deathmatch. Players can also trade mech designs and paint jobs.