Pros
Pay and benefits are great. Working here for a few years can set you up nicely for the future in terms of retirement savings. Some people are genuinely great to work with. Work life balance is decent based on what team you're on and what your management stack is like.
Cons
The main issue with McMaster-Carr is that it promotes people to leadership positions who frankly have no business leading people. There are a few members of management who care and support their team, but they are pretty rare, and the higher up you go the worse it gets. Toxic leadership who don't know how to manage people, only work, is the main reason the reviews for McMaster are so low. I don't blame them tbh, considering there is 0 incentive to be good people managers. Instead, the environment just incentivizes you to burn out your employees and make sure everyone but you is to blame if anything goes wrong. They mask the toxicity as "high expectations". If you give feedback about the toxic culture, they'll just say you can't meet the high expectations. Some people prefer this. Those are the people who last long enough to become promoted and perpetuate the toxic culture.