Pros
Important work that creates new technology, solves important problems - work with real meaning. Talented coworkers always have something to teach and to learn - collaboration is amazing. Equity packages with little risk and still lots of upside (even for new employees) Upper management is filled with super sharp and hard working people who care deeply about the success of the org and its people. They're not perfect, but the best I've ever seen. A great culture where people who want to take initiative are rewarded and lauded. The culture is protected and cared for to make sure this place doesn't lose its magic. A management team that's very introspective, transparent place always trying to learn and do better. A true meritocracy, where the best idea wins and seniority and titles are not important, just good work.
Cons
Some managers are sharp individuals but poor managers. Despite best efforts to train them, some folks suffer due to this. Company is growing fast and growing pains abound. The company is working hard to offset these issues, but new ways of doing things need to be implemented. Another growth issue: upper management is overworked more than anyone, leading to some pressing issue slipping through the cracks. They get fixed eventually, but there's pain in the meantime. People work hard and some groups try to maintain an unsustainable pace that leads to burnout and jealousy of people perceived to have "cushier" jobs. Overall compensation is high (due to stock options that are/will be worth real money) but cash compensation is lower than industry (not ridiculously so, but low, yeah)