Pros
Excellent coworkers! Working at SpaceX gives you the opportunity to work with some of the best engineers in the US. This combined with the "wear multiple hats" aspect of employment at SpaceX means that you get a lot more exposure than other employment opportunities and the quality of content that you are learning is just incredible. The work environment is set up so that you do not feel the long hours. If you are hungry, they always have food. There is pretty much anything to satisfy a craving while you are at work.
Cons
The barrier to entry for working on meaningful projects is quite large. It takes a solid 2 weeks to get all of the necessary information to do fairly basic tasks. All of the information is easily reached, but the quantity of material that must be known for every small step is burdensome in the beginning. The work is very interesting, and in my opinion makes the long hours very easy to endure.