Pros
Very Flexible and Supportive Environment, good challenging work if you work in one of the new technology development areas. If you work on the big programs it is less exciting but it is good steady and reliable work. I have to say Lockheed handled the pandemic well and in general respected and supported their employees. That support continues today with a much more flexible work environment.
Cons
Processes are not well documented and the usual ossification of a big corporation in terms of focus and pursuits. If you are looking for a more agile culture you may find it in one of the Corporate run labs but not in the main Business Units (Aero, RMS, MFC, Space). That said it is a big company so some groups within the Business Units are quite innovative and motivated. The company is good at what it does (defense systems) and as long as that is where you want to focus your career you will do fine.