Pros
Overall, Epsilon (I worked in their West Chicago office, formerly Aspen Marketing Services) is a decent company, with many good, hard-working people. However, the overall experience of any employee will always be directly tied to the team they are on, and specifically, the quality of that team's leadership. Comfortable work environment, pleasant atmosphere, free lunch every Friday, with the occasional internal perk (on-site flu shots, holiday themed mini-parties, etc.). Good amount of vacation/sick/personal time, ability to work from home based upon the team/account and your role.
Cons
The leaders of my former account lacked management skills and were only "leaders" by title, as they had no true leadership qualities. They were consummate B.S. artists, and had gained their position on the account by being with the company for 9+ years, while also becoming sacred cows, beyond all reproach or challenge. The team had 3 people request to leave the account (including myself) in less than 1 year, quitting due to the poor team leadership, not because of Epsilon overall. In addition, the client demanded that my initial manager be removed from the account (which she was), yet upper management ignored these red flags and kept the account management team in place. Shortly after I left Epsilon, they lost this client account. Lazy personnel decisions - instead of hiring someone to replace the lost skill sets when someone left the team, they drop the vacated responsibilities onto other team members, completely altering or eliminating the job the remaining team members were hired to perform. Structured or formal training does not exist in any format - all you get are rambling brain-dumps - better take good notes, and fast! Don't ask for confirmation of your notes either, as feedback is a long time coming, if you get any at all. Medical/Health benefits are comprehensive, but a bit more expensive than my previous experience, and more expensive than I would have expected them to be based upon a company the size of Epsilon.