when playing dvds and games, a 4.1 system is ususally great. but a problem is that the speakers in the rear don't have the aid of a subwoofer, meaning any explosions, or other low end frequencies are lost in the rear, thus a helicopter fly-around is much less impresive. with a 4.2 system and the additional subwoofer placed in the back remedies the situation. also in games with the bass pumped up, you can feel people walk up behind you!
if you got the cash go with 4.2