Those of you who enjoy racing games, what significant differences do you see between one racing game and another?

Obviously I'm not including burnout as the fun in that is trashing opponent cars while you're racing; for myself I enjoyed some of the earlier entries in need for speed (never played the later ones) cause I could crash into other cars and knock them off cliffs and beat them around to give myself an advantage; I just don't know what draws people to say for example Gran Turismo vs.....I don't know, I don't know any other racing games. Other than the 'crashing into other cars' factor, I don't know what the draw to one racing game vs another is.