Pros
I worked for Epsilon's agency services "subsidiary", and the place was crawling with talented people. Almost all senior leaders came from "big name" ad agencies and the strategy for most campaigns were quite sound. The businesses we were pitching for were fortune 500 companies and were all top notch Work/life balance was pretty good as well. I never stayed in the office past 6 pm, besides days or weeks where there was a big presentation or meeting. Office culture was pretty good too - the Monroe office has a large agency feel but a small office vibe.
Cons
One big con is that at its heart, Epsilon is a data company. When pitching new agency business, it seems to me like the company doesn't actually care about winning it, as long as some Epsilon data is sold. One other thing I had an issue with is that my direct manager didn't seem to know how to manage, especially someone with years of experience. I never had a talk about career paths, promotions, or any of the sort while I was there. I came in as manager level but was treated like an entry level employee. There's also no clarity on job titles. My role was changed a few months before I left to carry more responsibility but for some reason, there was no shift in salary