Pros
Working at MIT Lincoln Laboratory looks excellent on the resume. If you can get in the door it will definitely give your career a boost when you leave. While you are here, work life can be very laid back depending on the group you end up in. Other advantages are that you get to work with the best and brightest. Your work will also likely have a positive impact on your country. Lincoln Laboratory is excellent at training. There are many classes offered in house on a wide variety of fields. Additionally, the lab will reimburse you up to $5500 per year (the cost of a little less than 2 courses) for courses taken in pursuit of an advanced degree.
Cons
LL is a huge bureaucracy. There is minimal opportunity for upwards advancement. Unless you have a phd you will largely be held back by what degree you have. In my time there (5 years now) I have seen only a few people advance to higher positions within the lab. Speaking with coworkers I find that it is the general consensus that you can go up at most 1 level before hitting the ceiling imposed by your degree. Another downside is that there are very few women in the lab (outside of the Biology/Chemistry groups). I suggest you look elsewhere if you want an office romance. No stock options and pay is lower than industry.