Pros
The best reason to work at Lockheed Martin is because it's the best place to work for your first and last job. Lockheed Martin believes in having a well trained workforce and you will get a lot of great training and be exposed to a lot of different aspects within your career field. There are a lot of very experienced engineers who will impart their knowledge on you so they can have a lighter work load and feel confident that the company will have good employees to keep their stock value up once they retire. If you plan to stick with LMCO make sure you negotiate as much salary as you can. Many people take the job at lockheed and then quit to go work at a smaller company for more pay. It's hard to turn away work that pays sometimes 20% more! At Lockheed you can get a lot of exposure to some really cool programs that you'd never get working somewhere else (well maybe Boeing...)
Cons
The performance review process isn't the best. Only a small 4% of the workforce will receive an exceptional or high rating and the rest fall in "Successful" or "basic" which means even if you are a stellar engineer unless you do something great to really set yourself apart from the rest of the workforce your likely hood of getting a high score is slim to none. Get the best salary you can coming in the door because promotions and raises are small and few and far between. Lockheed isn't the place to come if you wanna climb to the top quickly.