Pros
3M has a great company culture. Everyone seems to uphold the companies values and in my two years working there I have not met anyone I wouldn't want to work with again. It is a large company so there is some "Bureaucracy" but I have never found it to hinder my job. The thing I like most about 3M is their flexibility in working and their willingness to do what is best for the employees and company rather than just the shareholders like many other companies in todays world. They are very "conservative" in their approach so don't expect crazy high salaries and crazy new world perks(like unlimited PTO, drinking at work, constant parties) but I have found everything about my job and its benefits to be fair or better than average. The most surprising thing to me about 3M is how many employees have been there 20, 25, 30+ years and still love their job, I think that is a testament to how well 3M treats their people.
Cons
I really cant think of very many cons. As mentioned before it is a large company so somethings are slower to move and you are usually defined by your role so if you want to do a lot of random unrelated things it might be tough too. Vacation is probably very industry appropriate but can feel like less compared to some other companies.