One of Doom II's most significant changes over its predecessor is that it takes place over a single linear sequence of levels - the episode-based structure of the first game was abandoned, as was the map shown on intermission screens this means that the player no longer has to find new weapons at the start of each episode. Technologically and graphically the game is identical, though due to more complicated levels and larger fights the base system requirements for the game were higher. To progress, the player must still navigate non-linear levels, find keys, and unlock new areas while defending against an onslaught of demons. In terms of gameplay, Doom II is similar to the first game, adding only incremental changes to its formula in the form of new monsters and a new weapon. Pumping his rockets into the creature's exposed brain, it dies, devastating miles of Hell's surface in all directions in its death throes, ending the invasion and giving humanity a chance to rebuild.Дoom II CD from the Depths of Doom collection. After finding the portal to Hell and returning once more to the underworld, the Marine eventually confronts the ultimate source of the hellspawn, a gigantic demon. He fights through the ravaged city, where Hell's reality is once again beginning to merge with our own, twisting and corrupting the heavily damaged ruins.

Left behind, he at first prepares for death, but soon receives a radio message from the ships' commanders that they have pinpointed the source of the demonic invasion not far from his current location. All of humanity's remaining soldiers make a desperate assault on the starport, but eventually they are annihilated and only the Marine remains.ДЇighting through the starport, the Marine manages to lower the demonic defenses, allowing the survivors to escape to the safety of space. Stepping through a portal to Earth which opens after the creature's death, however, there is a cliffhanger ending - it is discovered that the demons which invaded the Mars moonbases have now invaded Earth as well.ДЄfter Earth's major cities are left in ruins by the attack, the human survivors await evacuation from a starport, but the demons have surrounded it with a barrier of flames. The Ultimate Doom's story ended with the Marine protagonist's defeat of the second Spider Mastermind in a gateway between Hell and Earth.

How many missions in doom