Costco is overall a decent company to work with. However, the starting pay is not at all very good, it takes a while to get to a decent wage, get full-time work or benefits and the hours are pretty daunting if you work morning (you start at 4am).
Work is very fasted paced and depending on your position, very labour intensive. The management are all fairly friendly and they do have an open door policy.
Free membership, good management, benefits after some time
Poor starting pay, hard to advance