Pros
There are not many places you can work and actually say you're actively changing the human species for the better. SpaceX is one of those places. It makes getting up and going to work each day very easy. Management does their best to eliminate as much useless red tape as possible. It isn't zero, but for a company this size working on the type of projects they do, it is impressive how much they are able to both empower each employee to do what is needed for success while at the same time having checks and balances to ensure things are done right. We're working on the most powerful rocket and spaceship humans have ever built. Bigger than anything you can fathom. That's just cool!
Cons
As many will mention, the hours can be long and the work/life balance is less life and more work. As deadlines start to approach, the hours can start to get a bit intense. This is not a low-stress environment. You are directly responsible for your projects be it a success or failure. Must be able to cope.