The best thing that I learned at Walmart was that hard work was recognized and rewarded. I worked hard and came back during a break from college to be promoted to work in the photo lab (more responsibility, higher rate of pay). I also saw many full-time employees that I worked with move up to become department managers, assistant store managers, and even move on to the corporate office.
However, I also saw the opposite end of the spectrum. Some fellow associates seemed content to do the bare minimum and didn't go anywhere in the company because of it. In fact, they are still at the same level.
In my opinion, these are also the employees that you hear speaking negatively of Walmart's employment practices. They want something for nothing from the company and they aren't getting it.