Pros
Mercer is a good brand within its industry and employs some very smart people. They provide good client service. They promote people internally and grow people who are identified as high performers. The consultants are innovative and develop long-term relationships with many clients. Among its competitors, Mercer is well thought of.
Cons
Senior management fails to communicate honestly or frequently. To succeed there, one has to be willing to work very long hours despite the consulting firm's insistence that it values work/life balance. The company (and its holding company) are exceptionally top heavy. Mercer's billing rates are high, though on par with competitors. Still, as one rises within the ranks, he or she is saddled with such a high hourly billable rate that it's hard to continue to do any work for clients.