What I would keep/change

   As my project requires me to 'reimagine' the game, keeping the same title, I felt the most important thing to keep would be the 'feud' between two characters. The adaptation I would make on this is rather than have them as powerful sorcerers, I would have them as priests in a modern day (or perhaps 1980's) New York City, one of which has lost faith. They would both be tested by the Devil and BOTH be cursed with aging and told only 1 can survive. I chose this setting because the Catholic Church makes for a widely recognisable religion, and its Churches hold a great deal of reverence. It could also create the opportunity to have Catholic Churches as safe zones, replenishment areas and save points, which could also hide transitions where the last part of the map is deleted from the PC/consoles memory, and the next area is loaded, and therefore avoid loading screens. Churches would greet the protagonist with choir voices, and his timer would not go down while he is inside. The two characters could be brothers, however this is not essential, as the element of family is already created by priesthood.
   Another element I would keep would be the general camera. I would make the game entirely 3D, but have a 'from above' camera. This would need to be adapted of course, as the cameras in the original are essentially static, switching from area to area as you explore, and always from exactly the same angle. This was a very effective system at the time, but a modern audience would demand more exciting visuals, which this system would not be able to show. My adaptation would be to put the camera on rails. Most games which have this style of camera are very linear, such as Too Human, and Dante's Inferno. The system I would create is one where there are multiple 'rails' for the camera to follow, and there would be a drift from rail to rail, depending on which path the gamer would choose to go down. This is inspired by specific scenes from 2 separate films; Constantine, where John Constantine is storming the building towards the end of the film, and Silent Hill, where Rose is hiding in the bathroom from the men in hazmat suits. These scenes show what interesting and artistic effects can be created with a following rail camera. The main reason I would like to use this camera angle is because it could free up the right thumbstick/mouse for aiming, without turning the whole screen (similar to gameplay mechanics of Dead Ops Arcade in Black Ops). I am confident the loss of camera control will not take from the enjoyment of the game, as fairly recent games have this style of mechanics and are great fun and highly successful, such as Starcraft 2 and Diablo 3.
   Having come up with the basic movement, i thought about the rest of the core mechanics. Another reason I chose to make the characters priests was to create a gameplay model that would loosely resemble the original. Rather than combat, the protagonist would run from civilians who are unknowingly enraged by the presence of the antagonist and engage in exorcisms to increase the time he has left. This could get dry and repetitive though, if it is the only form of action to happen within the game. One way to avoid this could be to have a turning point in the game where fully fledged Demons openly spawn (emerge from manhole covers, jump through windows of boarded up buildings) onto the streets. These could be simply killed, either by shooting them, or using the environment, such as traffic or trash can fires. This could liven up the gameplay, as not all enemies could be dealt with in the same way, and Demons would create a break from standard humanoid opponents. This would all have to be set up in a way that is not offensive to the Catholic church. I believe this would be ok, as the player would be rewarded for essentially avoiding deaths, in fact it would be possible to avoid anybody dying in the whole game, assuming the gamer succeeds.