When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Rather that try to explain it myself I'll just direct you to this post by Talon90 that includes his explanation and pics from GM from the 2007 Bash (introducing he 2008 models). If you need more just ask.
As for "better than aftermarket", that depends on what you're after. Consensus is that it's as good as "most" aftermarket but not as loud as some. It's personal preference. The B&B Fusion is similar.
What is nice about the factory installed NPP exhaust option, is that you can add an aftermarket(like Mild2Wild) remote controller where you can drive with the valves open all the time(loud) and then be able to close them when driving on the highway around 1500 RPM. That eliminates the drone that occurs when lightly cruising around 1500 RPM. Most of the aftermarket systems are loud all the time, and have the irritable drone.
Believe me, it's nice to be able to drive with the exhaust in the quiet mode, yet have the option to go loud when you want to **** off the old bag that lives down the street.
With the M2W, when in the quiet mode, the valves will still open under aggressive acceleration.
I love the NPP... a nice rumble a low speeds... under heavy acceleration it sounds fantastic... just a roar, but while crusing at interstate speeds it won't give you a headache.