Pros
First of all, EY really means it when they say that they have a people first culture. Personally, the people aspect was very important for me before I started my career, as I truly believe that if you are not comfortable with the people you are working with, you will not be able to reach your full potential at work. Also, when it comes to flexibility, even at the staff level there is a lot of it. It doesn't matter what it is, the teams I have worked with have always understood and adjusted the schedules accordingly, so that the work gets done but the individuals also get to do what its important in their personal lives.
Kontras
One downside that I would say is not just relevant to EY but to all the big 4, and that's the insane hours. During busy season, there are times when you literally want to quit as you are working like 60 hours, including weekends. During these times, the people aspect becomes even more important since your team is what helps you get through the miserable three months. Another downside, which might not be a downside per se for everyone, is due to the nature of the profession there might be a lot of travelling and one might have to live out of a suitcase for weeks on end. That is a professional issue and again, is not restricted to EY only.