1] Believable physics, the car does the same things a real car does them when the driver does certain inputs to wheel & pedal. 2] FFB, the way it communicates through my wheel (T500) telling me what the car is doing. 3] Immersion, the way the entire game sucks me in strings me along suspending all connection with the real world (until my wife calls me to dinner). 4] AI, better and more believable than anything else on the market right now, and probably better than anything else that has come before. 5] Dynamic track, realroad is a game changer for sims and all racing games. 6] Dynamic environment, actual day/night cycle and changeable weather (still wip but getting there). Looking forward to the addition of heat, humidity and wind effects. 7] Tyre model (actually physics but deserves a separate mention), the way this awards good driving and punishes bad driving through flat spots, heat buildup and wear. Even though my own driving can be labelled as bad more often than not. 8] Packaging & Installing, the system created by ISI has taken the genre to a whole new level, despite the nay sayers, taking a lot of guesswork out of introducing new players to the genre. 9] Modding, open platform and still doing it better than the competition. 10] Graphics !! Someone had to mention it, ISI are doing wonders with the platform they stuck with (initially to support the still large XP contingent).