Incredibly varied experience depending on team
Pros
You will be challenged, whether it is figuring out how to manage your professional development, dealing with difficult clients, balancing multiple projects. ZS will throw many issues your way, and many times you will need to solve them, though there will be people available to support you. This makes for great storytelling if you decide to leave or go to business school. While ZS doesn't have a super strong brand outside of pharma, the problem solving you learn will be transferrable.
Cons
Not everyone has your interests in mind. If you don't actively have conversations about promotions and projects, you'll be stuck where you don't want to be. Project experience is still driven primarily by staffing need. Because of the offshore team, you also might not get the extensive technical skills you want, such as in Excel or analytics, because it's just easier to hand it over to them, especially when things get busy.