DOOM II isn't exactly what I'd call a massive overhaul of DOOM (the original). It doesn't change up the graphics in a major way, nor add anything that could be seen as a major upgrade to the gameplay. They didn't even change the hud for the game. However, what DOOM II lacks in technological advancements it more than makes up for in level design. The devs took everything they had learned from assembling the first DOOM and took it to make a game more focused on open-field combat with large amounts of enemies. Even the earliest levels, which seem to tap into the spirit of the original DOOM with cramped hallways and interior levels feel far different from the previous game. Interiors feel more winding with space to open up into smaller arenas- a staple of later shooters. While the middle of the game does sag quite a bit, the scope of the levels cannot be ignored. The all-star addition of a super shotgun is awesome and rounds out the weapon spread nicely enough, although I wish there was more the devs could've added to the arsenal to further expand upon it- but that's wishful thinking for more content that may have impacted the game negatively. The enemies go a long way to spice up the variety in the combat, I only wish the Archvile got a little more screentime, but I'll call it forgiven because the Revenant is a somewhat common enemy; however half a star gets taken off because of the Pain Elementals. (I'm that petty.) Regardless, it goes without saying, but Id outdid themselves in making an expansion truly worthy of being the original's sequel. No overhauls or fancy new engine were required to the make this game great. It supports of the age old adage: "if it isn't broken then don't fix it."