Pros
Lockheed Martin is a great stepping stone in your career and if you are mission driven/mission focused you will find a place here -- up until a point. Depending on your program, experiences may vary. LM is never going away, and the products are very meaningful to warfighters.
Cons
One of the most top heavy leadership models you will ever see. High attrition. Results driven to the point where younger, talented engineers can be treated like workhorses and few senior++ engineers are doing almost everything. Knowledge is siloed, very imbalanced, and the culture is nothing to ride home about. Inefficient, bureaucratic process cause a lot of waste, engineering culture is more about self-driven ego rather than contributing to the warfighter and objectives. Overall, LM is able to extract really big money contracts to work on efforts, employ a lot of people, charge them as resources, and make a lot of profit as a company. This profit driven model overshadows the mission driven focus and the organization is a clear reflection of that.