Pros
There are several opportunities to change jobs frequently if this is what you enjoy. Contracts come and go which may be a CON for some. If you have been identified as a high-potential leader, adjacent opportunities will surface. Lockheed has a history of innovation and developing cutting edge technology; think: Mars Rover, F35, Cyber Security and many more. Probably some of the smartest people I know work at Lockheed. LM is also the most ethical company I have ever worked for and while there may be examples otherwise will deliver what it commits to customers. I have seen them lose millions on contracts to meet deliveries where others may walk or deliver half-baked solutions.
Cons
Lockheed is a typical fortune 50 business with a large bureaucratic system. Getting things done can be difficult although this has improved over the years as portions of the company have contracted due to smaller government budgets. Lockheed is very structured with a lot of individuals in support functions which could be seen as a PRO for some.