Pros
Everyone here is working toward the same goal. I am surrounded by people that are smarter and more talented than I am, people who are helping me learn and grow much more than when I was in school. I am challenged by my work, and interns here are given mission-critical projects. It's clear that the employees here genuinely love their work and the mission they are working toward. There doesn't seem to be a whole lot of politics--most people want to stay close to the engineering role they were hired for. My department is trying to foster a culture where people have opportunities to change roles when they feel like they aren't growing any more. Things happen INSANELY quickly here: one week someone will be designing a tool or a part, the next week it'll have been manufactured. It's amazing to work at a headquarters with such tight integration between design and manufacturing. Elon is truly a world-changing CEO, and it is exciting to work for him. And of course, it's an awesome feeling to come to work every day and build rockets!
Cons
There aren't established methods of communication. This is partly to do with how quickly SpaceX grew in the past few years, so I hope this will continue to improve. Groups are sometimes adversarial with each other, and sometimes cooperative. People get frustrated when requirements change, and it seems like most groups are still iterating on how to structure their communication. Managers are often protective of their employees' time because people can easily be overburdened by requests from outside their group. Beyond the communication stuff, we are ALWAYS crunched for time. Everyone here works long hours on short deadlines. Working here definitely requires a conscious choice to accept a demanding schedule.