Pros
Flexible hours help if you're not a 9-5 kind of person. Office location is convenient for commuting.
Cons
The culture is permeated with politics, passive aggressiveness, bullying, and resistance to change. Some people are held accountable and others aren't, which is demoralizing, and it's very apparent as to which functions in the company are valued and which are not (soft skill jobs). Slow promotions make it even harder to deal with the environment. Benefits are also not great - expensive to fund an HSA plus pay a still fairly sizable premium and then pay fully out of pocket because not a lot of doctors in MA want to take United. If you go to work just to collect a paycheck, you're fine, but if you want fulfillment in your work and to feel valued, it's a hit or miss depending on your department and appetite for playing politics.