Pros
I can really only speak for the research-related parts of the company, but Pioneer has great work/life balance and still has good benefits despite some cuts last fall. I work with intelligent people on interesting projects. Leadership listens to lower-level employees and there's little top-down management for a company of its size. Revenues have dropped in the industry lately, but the long-term outlook for ag/biotech is great. Des Moines is also one of the best small cities to live in overall. The workforce is culturally diverse. The hiring manager handles the most important parts of the hiring process, and HR isn't overly involved.
Cons
There are a lot of cooks in the kitchen in research, and leadership has trouble making decisions because real authority and influence is relatively diffused. The org chart is pretty complex. In some cases, maybe there should be more top-down management! Poor performers aren't held accountable very well, and usually just shifted around from team to team. You would have to do something outrageous to get fired. DuPont leadership seems far removed (physically and otherwise) from Pioneer. Their attempts to integrate Pioneer further within the larger company seem to introduce more bureaucracy.