In 1999 aliens attack earth, destroying major cities and wreaking havoc everywhere. Four total badasses take it upon themselves to stop this, loading up on guns, whiskey and cigars and take the fight to the aliens.
Operation Hardcore is a run & gun platformer with some modern touches such as twin-stick 360 degree aiming. There's a focus on physics: firing your weapon will push you away with recoil, power-ups fall, roll and pile up, shooting enemies will bounce them around and so on. Some levels strap a jetpack to the player and instead have you fly through these sections.
Additionally the player can double-jump, drink whiskey to slow down time, and finally has a manually activated bubble shield that makes him invulnerable to all damage (except bottomless pits) but needs to be recharged by picking up rare shield pickups. The shield is useful in combat, but can also be necessary to pass certain obstacles, like fires. These obstacles always have shield pickups nearby.
Killed enemies or destroyed crates might drop coins - money can be spent in between levels to upgrade weapons or purchase weapons and limited power-ups. Other than your starting pistol there are four other weapons - machinegun, charge-up laser, flamethrower and spread gun. The first three are granted by picking up a cycling gun pickup, while the spread gun is generally placed in hard-to-reach places.
Dying will respawn you near where you died, but you will lose your weapon (if any) and go back to the pistol. Running out of lives will (on the easier settings) send you back to the start, losing your powerups and upgrades, but regaining some of the money depending on the setting.
There are three game modes - regular, hardcore and challenge levels - and four difficulty settings with varying rules regarding number of lives and pickup values. The game can be played with one or two players.