Last Sunday night, Bethesda released a free demo for Doom that lets players check out the shooter's first level. It was only supposed to be available the week of E3, but now, developer id Software has announced that it's being extended, though it's unclear for how long.
Whatever the case, you can grab the demo right now for your platform of choice using the links below.
The free Doom demo is for the game's campaign only; there is no multiplayer.
Doom was released in May to a great deal of acclaim for its single-player mode. The multiplayer mode has faced some criticism, and at E3, Bethesda announced a number of new features are coming for Doom's multiplayer in the form of free updates and a paid DLC pack.
Executive producer Marty Stratton told GameSpot at E3 that id Software is considering adding a Rocket League Rocket Labs-like "experimental" playlist whereby new modes and features can be tested before they are rolled out publicly. As for more single-player content, Stratton also told us that id Software has "a couple things" in the pipeline that will be announced "shortly."
from GameSpot http://www.gamespot.com/articles/free-doom-demo-extended-heres-how-to-play-it-right/1100-6441058/