An M rated game?
Man, thats totally hard, I can only think of a few...
Resident Evil 4 if your really into 3rd person shooters, or possibly Resident Evil: Darkside Chronicles is fantastic if you love rail shooters, if you end up getting Resident Evil: Darkside Chronicles I suggest getting the Wii accessory "Perfect Shot" it looks like a gun and makes rail shooters all that much more fun!
You may like Tenchu Shadow Assassins it runs pretty cheap now a days, I think 19.99? Its a 3rd person Ninja game.