Pros
Legacy TW had a good reputation among clients for producing high-quality work. I saw high standards for work quality. I also met amazing colleagues. Very quickly, I became proficient in analytical tools. I also learned a tremendous amount about retirement plans (particularly traditional defined benefit pension plans).
Cons
This company is in transition. The truth is that traditional defined benefit pension plans are declining in the US and in many places in the rest of the world. Long-term, most people expect a decline in revenue from the core TW retirement business, in part because legislation and taxation been unkind to pension plans. The retirement practice was siloed from the rest of the company, so it was exceedingly difficult to transition into another line of business. I always thought retirement actuaries were very cliquish and spoke in too much jargon. It probably is an exciting company to work at if you are in health benefits/exchange. Senior management has steered the company in the direction of brokerage services/healthcare, which I think is probably a good decision. They definitely took risk to do this by merging with Willis, which serves mainly small and mid-sized clients in the US (and was highly leveraged). I got the sense when I was there that senior management quietly let attrition occur among mid-level employees in retirement, which given the long-term outlook of the business, is probably the right decision. Just be careful before taking a job in a core business at Willis Towers Watson if it is in a revenue-declining segment. This is true of retirement, but might also be true of other lines such as risk and financial services.