Avantages
Lockheed is stable in an unstsable economy. Because of it's size, we are able to weather problems in an unsettling time. When a program is cancelled, we attempt to shift employees to another project. We'd rather keep employees than lose them. That is partially biased for working for LMSSC in Huntsville, AL, but I assume that all locations would share a similar ethic.
Inconvénients
Lockeed Martin, like many large organizations, has a dual career ladder. The technical side is somewhat short and pointy - not much room for growth there as "there can be only one." The management side has more opportunity, but once you cross into functional leadership, you're taken away from all things technical. There is a 1/2 ladder associated with the techncal side (technical management), but it's also very competitive. Really, it's a stable place to work but you don't expect to stay here for 30 years and get to the top.