Twilight: 2000 is a complete role-playing system for survival in a devastated post-holcaust world. Rules cover character generation, living off the land, encounters, combat, skills and skill improvement, medicine, vehicles, ammunition, trade and much more.
The combat rules are a major breakthrough. One general combat resolution procedure covers all types of combat: hand-to-hand, melee weapons, small arms fire and fire against armored vehicles. Once the basic three-step combat sequence is understood (Did you hit? Where did you hit? How hard did you hit?), combat is quick and easy to resolve, but the wide range of weapons values keeps the system rich in detail.
The background to the war is covered in detail, and extensive material on the state of the world is included to assist the referee. The beginning adventure is actually a campaign and is the most complete adventure of its type to appear in a role-playing game. It not only gets you playing quickly, it provides many gaming sessions worth of encounters and andventures and then easily blends into your own campaign.
Game charts are in a seperate chart booklet, and are arranged so that each two-page spread of charts contains all the information needed to referee one aspect of the the game (travel, encounters, personal combat, vehicle combat, etc.) so there is no flipping back and forth searching for the correct chart during play. from the referee's point of view, it is a very user friendly game.
There's a wealth of information about Twilight: 2000 version 1.0 in the DTRPG Guide to Twilight: 2000 version 1.0 (free download).