The Mongoose bikes sold at wal-mart and the Mongoose bikes sold at actual bike shops are NOT the same bikes.
The ones sold at bike shops are actually pretty decent bikes. It's no Cannondale or Kona, but it will be lightyears ahead of the Wal-Mart bikes.
Basically, they produce two lines of bikes: one line of cheap, crappy bikes that they market to big box stores like wal-mart and academy sports, and a totally different line of good bikes that they sell to bike shops.
The Mongoose you buy at an actual bike shop will be a good, quality bike that will not disapoint you in terms of its quality.