Pros
SpaceX will provide you with a feeling of deep fulfillment that makes the work you do feel like the most valuable work you've ever done in your life. You'll find yourself talking about work, even when not at work, becoming passionate about industry and doing everything you can to help the mission succeed. In return, SpaceX will give you the opportunities that you never even knew you wanted - you'll feel empowered to continue to learn within and outside of your area and to make change wherever you see improvements needed. You'll have coworkers who you'll become really close to where you end up spending time with them both inside and outside of work. You'll cheer in front of mission control when you help make history and you'll raise a glass with your coworkers when you have to say the phrase, "Rockets are hard." Overall, this place will change your outlook on life - and what other company can you say has that effect?
Cons
SpaceX will consume your life - if you let it. It's up to each individual person to figure out a work/life balance and if you aren't aware, you'll be pulled into the center of SpaceX and start wondering where all of your time went. However, stay aware of this and keep reasonable hours and you will be able to keep a healthy work/life balance. Also beware of the freshmen 15 - but this one is in terms of relationship danger. Starting to work here, you'll find yourself swept away by all that is SpaceX and that can end up weighing heavily on relationships. Make it through the first 6 months and your relationship will come out stronger on the other side - but it is just another thing to be aware of.