You actually have to work to drive the car in FM4, GT5 is very predictable and the only challenge was if you were using the comfort tires. The lower class cars are actually fun to drive in FM4, and the AI can be a challenge here. GT5's AI is just a bunch of moving chicanes.
The car selection is much better here, i have no use for 20 versions of every Nissan made between 1980-2007. GT5 may have good graphics but FM4 isn't far behind and looks really good to me. Besides it's game play that makes the game, not the correct stitch pattern on the seats of one of you sixty Skylines.
Over all FM4 is a much better game, I should have done this long ago.
Also i play with the controller, I'm 34 so thats just what i'm used to but may be getting a wheel some time in the future.