Ventajas
To me, in the world of healthcare PR agencies, it would be hard to top GCI Health. Highly competitive compensation and benefits, strong leadership, passionate colleagues, a wide range of clients with rewarding work, and flexibility to work from home or in the office as you wish. While I can't speak for every city, the NY culture team has done a good job organizing a range of social events, including happy hours, fitness outings, volunteer outings, a new book club, etc. And I honestly just truly enjoy so many of my colleagues on a personal level.
Desventajas
IT issues can be fairly widespread though they are doing their best. It's not GCI specific, but a broader WPP issue. Like any agency, work-life balance is mostly dictated by who your clients are and their needs of the day. That said, I've found senior staff to be pretty vigilant of others' workloads with many having a "roll up your sleeves and get the work done" attitude regardless of your title.