NFS is the first sim I ever bought and still have a soft spot for it. I found the dynamics of later NFS sims unrealistic, same with Test Drive and the GT(1,2,3) for PS are nothing better than arcade games for little boys
For my money you've got to go for the TOCA (2, or later) touring car series - the game engine is fantastic, dynamics are realistic and the cars sound like the real thing. I'm also a big fan of Sports Car GT and Le Mans