Pros
Great place to work, especially for those just starting their careers and interested in pursuing professional credentials (e.g., becoming Assciates or Fellows of the Casualty Actuarial Society, CPCUs, etc.) Great people to work with -- as rule, very smart, very dedicated, and very collegial. Good work / life balance (for those who don't get too fascinated by what they do.) Great business problems to work on (at least, in the spot I had.) Relatively free of office politics -- you can win an argument by marshaling the facts and getting the logic right -- doesn't depend on who you play golf with. Good opportunities for advancement if you pay your dues / generate value.
Cons
Like all complex organizations, subject to periodic reorganizations and the risks associated therewith. Senior management can be a bit arrogant at times (as a result of their success running the business, I think; I give them a pass on this because they are "justifiably" arrogant, as opposed to those that are "baselessly" arrogant.) Some have reported that entry level work can be less than exciting (though , for toise that are good, that changes).