Avantages
Lockheed is serious about doing the right thing. It is in my experience extremely rare to find a manager to ask you to do anything shady. They are receptive to employees wanting to obtain opportunities to learn new things - rotate in jobs, receive mentoring, and there are programs and opportunities where the company invests in the employee (how I got my MBA paid for). The culture is to work hard and get the job done right.
Inconvénients
Like any huge company, they are bureaucratic. You have to be sensitive to the chain of command - stepping outside that chain or not taking proper care to understand what is expected within that chain of command can get you ostracized fast. Decision making often requires multiple levels of approval which makes the company safe (sometimes too risk averse) but also time consuming and expensive to get decisions made.