Ventajas
LM offers very flexible schedules so it's great for people with families. LM Space at least doesn't have very stringent acceptance criteria so it's pretty easy to get a job here. Especially if you have a clearance. You will meet a lot of great peers here and build lasting relationships that are great to have in your network. The employee resource groups are also great to participate in and meet others with shared values or interests. It has been amazing to see an increase in diversity amongst the VPs at LM. There are great rotational program options to help gain breadth in your work experience. It's very easy to coast here. Doing your job verses doing your job well rarely has a different result, even when it comes to promotions and raises. If you're looking for no stress, decent salary and benefits, this is the right place. The concept of everyone gets a medal has been very prominent throughout my career.
Desventajas
The leadership is pretty hit or miss, mostly miss. Very few prioritize the employees. Schedule and cost will always win over technical. Leaders stay in leadership for a very long time, seemingly regardless of performance. While you will meet amazing people, you will also meet more incompetent ones, or rather unmotivated employees. I would not recommend LM as the place to accelerate your career, the opportunities to climb are far and few between. It's also very easy to get stuck working on projects with experience that won't transfer to other companies outside the DOD very easily. I have no kids so am perfectly willing to throw myself into work to excel, but here that doesn't buy you anything.