DEFCON is a strategy game dealing with nuclear warfare. You have a flat map of the world that you can scroll and zoom, and the graphical style gives the impression you are planning your nuclear attacks via an old computer. The items that you can place are simplistic icons and the aircraft/nuke's trajectory are plotted with dotted lines. The graphical style is minimal but definitely functional.
Each player takes control of a single territory which are roughly based on the Continents; North America, South America, Europe, Africa, Asia, and the U.S.S.R.
Unlike most strategy games, there are no economics to manage, putting the focus solely on warfare. You only need to worry about initial unit placement, then attacking and defensive strategy as the game progresses.
The game has 5 phases which are declared as DEFCON levels. DEFCON 5 is when you place your units. Radar stations aid detecting enemy units, Silos function as either anti-air or missile launch sites, Airbases can deploy fighters and bombers, fleets of ships can be created from battleships, nuclear submarines and carriers (which can also launch aircraft). You can continue building into DEFCON 4, which is when your radar stations will function. In DEFCON 3, the build phase ends and the focus switches to exploration with naval units. DEFCON 2 is more of the same, but you have to wait until DEFCON 1 to begin deploying nukes. The transition between each DEFCON level is timed, but DEFCON 1 lasts until there are only a small percentage of nukes left to deploy. At this point, a count-down timer begins to conclude the game.
Destroying enemies units gives you a tactical advantage and can swing the battle in your favour, but the main aim is to score points by hitting enemies' cities. You can always see cities on the map, but seeing enemy units is reliant on radar coverage. In addition to the radar units you put down, you can take advantage of naval and air units to gain extra visual coverage. The exception to the rule is when any unit launches a missile, the launch is announced to other players which uncovers the place of origin.
Nukes take a long time to reach their destination, so you need to make sure they hit their targets. You will need to co-ordinate launching nukes with other silos/submarines/bombers to maximise damage. You will need to try take out your opponent's silos to reduce their anti-air capabilities and stop them from launching nukes back. Fighters will need to engage enemies fighters and defend against bombers.
The audio is fairly minimal, but it creates a chilling atmosphere with the sounds of people's cries and coughs. The sound, in addition to text such as "1.8 million dead" which pops up really make you feel guilty about firing your nuke's towards civillians.
The game's manual has the obviously useful stuff about the game, but also contains information to build your own fallout shelter and suit; just in case you are involved in a nuclear war!
DEFCON may have only a few units, but contains a decent amount of depth once you get to grips with the mechanics. The game is fairly slow paced, but you can change the speed on the fly. DEFCON is designed as an online game, but you can tinker with a few options to set up a local single-player game if you wish. Without a dedicated single-player campaign, there wasn't too much to keep me interested. It's decent enough, but I'd really only recommend it if you have the ability to set up multiplayer games.