Pros
WTW is a large company, and experiences will differ greatly between lines of business, some of which have never and will never cross paths anywhere below the executive level. Within the benefits outsourcing business, a client team developer will find a supportive culture and often challenging work, at least with respect to the unique aspects of the benefits business.
Cons
C# developers tend to be paid less, and for good reason. .Net and C# are designed to have a fairly short learning curve when utilized within a well-defined system. You aren't going to get serious coder chops working here, at least not within the first several years. The benefits business runs on an annual schedule, so forget about fall getaways as that is the busiest time of the year.