Pros
The benefits are great and extensive. The salary ranges are very competitive and they are willing to negotiate with you to remain flexible within reasonable expectations.
The culture is innovative, forward-thinking, fast-paced (seriously...it is), and open-minded. All of my previous employers acted like they valued your opinion or suggestion to improve a process, but ESI really does take it into consideration all the way up the chain before a decision is made. You have a voice here, and that's really impressed me. A plus is that the whole entire campus is brand new (2007 and newer) and state-of-the-art.
Never a dull moment or shortage of work to do. On that note, outside people hear a lot about work-life imbalance at ESI, but I just don't see that. Every single person here pulls their own weight in the same direction working toward a common goal, and nobody gripes about it. You can see people genuinely care about their work, and it's shown objectively when just about everyone regularly hits 100% or more of their annual bonus plan. I don't know about you, but I'd rather HAVE work to do than sit at my desk all day and have nothing to do (been there before, it's miserable). A lot of the mixed reviews I see are from the frustration of the constant integrating and merging of newly acquired companies' employees and processes, which is understandable, but the focus is definitely changing to efficiency and making work/life easier. I believe if there is a work-life imbalance that it is silo'd into certain departments, but it's certainly not a company-wide issue.
Cons
Not really any glaring Cons, I just think people need to socialize a little more. Everyone works hard and has the go-go-go mentality, but it wouldn't hurt to loosen up and have a little fun here and there.