Pros
High profile clients with frequent exposure to client senior management. Engagement experience from many businesses and industries. A lot of responsibility for the deliveries early on. Steep learning curve and work is almost never dull. For the most part intelligent, social and fun colleagues to work with. Big 4, including KPMG, looks good on your cv when you move on.
Cons
Depending on your department head, engagement partner and/or performance manager/coach, office politics could be an issue, as anywhere else. Focus on sales and billable hours occasionally takes precidence over communicated corporate values, such as work/life balance and cooperation between staff/departments as at any other consulting firm. Being a consulting arm at an audit firm adds extra red tape and restrictions to engagements, (however manageble). Salary could be more competitive. You need to be prepared to put in the hours at times.