Any racing game with an in-game credit system to buy cars and upgrades, I keep playing them for fun if they're already at 100% and took me a month at least to get it (I'm such a racing game madman, that I totally shred many racing games in days).
And if that 100% took me only days, I start them all over again with different cars.
Midnight Club LA was the first game with that I got on my XBox 360...but I hated the fact that by the endgame, money is pointless, as after the 1 million thing, you get everything for free.
But then came Forza Motorsport 4 and the vice began once again lol