Ventajas
Lockheed Martin is a fast-growing company, with plenty of diverse job opportunities in all sorts of areas, from Procurement to Compliance to Engineering (of course!). A sizeable chunk of its workforce of 140,000 people is retiring within the next decade, and there are going to be many openings to fill when the baby-boomer generation leaves work. While Lockheed's benefits may not be as good as they may have been - mostly because their pension benefits have been eliminated like at most other firms - they still provide a very competitive package along with generous pay. Another reason to work here that may appeal to some people is the opportunity to move around to various offices around the country. With 60+ offices scattered throughout North America (the US and Canada), offices in the UK, and even one in Argentina, there is sure to be a location to match your needs and interests. The people have been very nice and helpful in general, and I find that there seems to be a minimum of backstabbing and other devious behavior.
Desventajas
Like any other large corporation, there are going to be distasteful aspects. One for me has been the sometimes ridiculous amount of time it takes to get people to do things. The bureaucracy can be intense, especially since Lockheed Martin has to abide by so many government rules, regulations, and restrictions. For example, getting a very basic security clearance took weeks if not months, along with me having to fill out piles of paperwork and an EXHAUSTIVE life summary. I'm surprised that anyone can remember that much information, and the only reason I was able to is because I've kept detailed records of my employment history and other things. Another somewhat annoying aspect has been staying busy at all times. It sometimes seems that everyone is too busy to really sit down and talk with the interns. However, to give the issue justice, everyone probably IS really busy, and there sometimes is a good level of fun and games in the office that helps liven up the mood and keep everyone friendly.