The company is very old fashioned in a lot of ways. It means they are very focused on customer service (good), but there's very little mixing between management and non-management. At a lot of companies, if you start on the bottom rung and work really hard, you could eventually get promoted up the corporate ladder. At McMaster-Carr, you if you start on the bottom rung and work really hard, you could eventually get moved to a rung a little to the side, or a rung on another ladder or a rung a little bit above yours. But if you aren't hired into the company as a manager, you will never be management. That's their policy, not just my opinion.
Most of the management trainees, your bosses, are just out of college. It's pretty common for McMaster-Carr to be the first real job for some management trainee who just finished their Ivy League degree. It's their first job, and they're trying to "manage" an employee who's been in the workforce over 15 years.
McMaster-Carr doesn't invest in training non-management employees. When a non-management employee starts in a new role, they shadow someone in that role for about a week, and that's it. Even if the new role is in a completely different area of the organization, you get about a week to get up to speed, and then you need to hit the ground running. In some areas, because there's such a lot of turnover, this is really a problem.
McMaster-Carr is also a pretty lean organization. That means that the longer you're there, the more work you get. But since you can't work overtime, you're trying to fit more and more work into the same number of hours. The people who are management, because they've never actually done your job for longer than a couple of weeks, and because they rotate every 6 months to a year, don't really understand what you do or how long it takes you to do it.
The actual day to day work that you do is very mind-numbing. Again, this review applies to people who aren't management. If you're in the warehouse, you're filling orders or packing boxes or shipping material and you're not allowed to make mistakes. If you're in the office, you spend your time doing small, repetitive, mindless tasks. Management places a lot of importance on tiny details. It's in the name of good customer service, but it means that they (and you) end up wasting a lot of company time micro-managing.
As a whole, the company is very reactive and not very proactive. If you aren't management, you can point out a problem and offer a simple solution until you're blue in the face, but they won't listen to your suggestion until the branch manager notices something is wrong. Then they'll have hours of meetings and come up with some cock-eyed answer that creates more work for everyone. It's frustrating that so many managers are incredibly book smart, but don't seem to have a lot of common sense.
If you're at a point in your life where you're ambitious and you want to advance your career, if you don't care how much money you make, or the amount of time you spend in the office, as long as you can do work that's interesting and meaningful to you, McMaster-Carr is probably not the place for you.