One of the forefathers of First Person Shooters, Doom can be one of the most fun, challenging, games, youll ever face. Whilst Doom alone is not renowned for its difficulty, take a moment to wander into nightmare mode where once there was an enemy, now there are fifty and where once there were numerable health packs, now there is only the will to survive. Nightmare mode is a visual representation of hell, so massive is the volume of firepower you can come under, youll have no idea what colours the walls are until theyre stained red with your blood. Its a difficulty setting made for the hard-core, that, if you do manage to hold your own for a few levels, your heart will have probably gone into cardiac arrest and as you keel over to the crushing sound of overwhelming, enemy fire, you will know you were never a match.