Pros
Working with some highly motivated people - many among the leaders in their fields - to help actual humans with their actual lives rather than just a bottom line (although hospitals have bottom lines, too). Solid benefits. Good location. Generally collaborative work environment. MGH is within the Partners network of hospitals, so you are part of a larger community than even just the massive MGH campus. One benefit you won't find listed anywhere: Since so many things in life come down to relationships and networks, being in this community could give you a leg up if you have a health issue, as you will likely know doctors who know other doctors... to the point where you might more quickly be able to get in front of the best person to be treating whatever ails you. I'm not saying that in a nefarious way, any more than saying "If you work at TD Garden (or Gillette Stadium or Fenway Park), you're more likely to run into world-class athletes and musicians than the average person." This healthcare connection is not so much cutting the line, as smoothing the path.
Cons
You could be an accomplished career professional in a non-clinical field, but you will always be "support staff". An experienced JD/MBA would be outranked by someone whose new white coat just got their name stitched in that morning. That seems to be true regardless of the topic of conversation. While everyone is an individual, each handling interpersonal relations in their own way, the infrastructure of the hospital was (understandably) made by doctors, from the perspective of doctors, for the purpose of doing the business of doctors. The result is that if you are not a doctor, you are "support" - and your work matters less (or is perceived that way by the hospital at large). Sometimes the MDs even look down upon the other types of doctors (PhD, EdD, PsyD, JD, ...) in the same way that the general public might say to a PhD "Oh, you're a 'doctor', but not a *doctor* doctor..." I was also told that people (esp. clinicians) are often paid less than market value in trade for the prestige of working at MGH and, for clinicians, the Harvard affiliation that may accompany it.