Pros
For some reason IBM attracts really great people to work with. Really smart. If you go to work there with the attitude, "What is somebody going to teach me today?" you'll meet some incredible technical practitioners. You'll keep them in your professional networks forever. for early career, it'll look great on your resume.
Cons
Huge cultural shift over the past 0-5 years where the employee is just a commodity. You are nothing else but a commodity. You can be the hardest worker; you can get great performance reviews. But if you're in the wrong place in this vast company, and your data points turn up positive in an algorithm selecting employees for layoff, you will be hit. No quarter. All cards are stacked against you except if you are college hire to mid career lower salary. As an individual contributor (less if you are a manager, but still happens), you will be eventually laid off. So, employee culture is pretty much hollowed out -- lots of grim faces because of the packed conditions in the office, rolling layoffs, and RTO mandates. So sad, but true. I hope IBM can find its way again and start investing in people by letting them grow a career there again. But the powerful short-term (Q2Q) financial chess game rules at IBM. You'll run into some wonderful people there, tho! The best!