Pros
The best reason to work for LMT are the projects we do. You can't work on the kinds of things that you do here anywhere else. Want to work on Manned Space Flight, Planet exploration or an important defense project... this is the place. The technical challenges are tougher than anywhere else I've worked. The sense of purpose is also stronger than anywhere else. It's important to realize too that LMT is really hundreds of companies under one name (the product of 20 years of M&A). If you feel stuck or don't like the culture at a particular position and you work in an area where LMT has a couple of different operations you can move on, and often find a very different experience somewhere else. That sort of flexibility is really nice. Finally pay is good, benefits are excellent, and paid vacation is excellent. Flex work schedule is also excellent. If you just look at the pay you're not going to be blown away. But remember that generally overtime is paid even for salaried positions, which means you work less of it, and when you do you get paid.
Cons
I once tried to count how many levels there were between me and our CEO and I came up with 11. I've never met our CEO. Keep in mind what I wrote in "best reasons" which is when you work for LMT you're really working for one of the hundreds of companies that LMT M&A'd in the last 20 years, with easy mobility between companies and a uniform set of pay/benefits and schedule. This creates to put it mildly a political and beauracratic challenge. Want to get good a negotiating a beauracracy... this is the place for you. I suspect many jobs have this challenge but I'm guessing it's more acute at LMCO. The other chief downside is the cyclical nature of our work. To survive here you have to realize that you are a contractor, and you are selling your services to a project. When the contract goes away (and it will, and it may go away at a senator's whim) you need to quickly find the next contract. Lockheed is supportive, but it's still nerve-racking knowing that you have an expiration date at the end of a project.