Pros
Palantir will challenge you. If you want an employer that will let you explore your ability to build, learn, [sometimes] fail, and grow as an engineer, Palantir provides. Opportunities to take ownership and do something awesome (both mission and technology), are everywhere. That said, you have to either take them for yourself or proactively work with your lead as there are no set paths for career growth. Related to no set paths, Palantir truly understands that every employee has his/her own strengths and weaknesses. While there are titles and defined roles, most are filled by a wide variety of people who specialize in various different ways within the role. If you're smart and have good judgment, Palantir has a place for you where you will get to build what you're good at and be valued for it. The mosaic of employees is exciting. Palantir of course has it's fair share of university built computer scientists, but I regularly have the opportunity to talk with physicists, ex-military, comic artists and other varieties of people. Basically because we work in so many different areas of the world (healthcare, energy, defense, anti-money laundering, etc.), our employee diversity matrix is incredible and unrivaled. In all honesty, I think this is my favorite part about Palantir; there are fresh, interesting people everywhere.
Cons
Some days are exhausting. With the chaotic "take ownership" nature of the company, it can often feel like guidelines are missing. Your fate can be in your own hands especially with a newer lead. You need to make sure your lead understands your skills and wants, so that he/she help you find the opportunities and problems you want. There are no checklists for promotion or growth which can suck, but also means bureaucracy won't hold you back. This is the chaos, but it comes with so many advantages I think it's worth. Work-Life balance is in your own hands. Many people in the company struggle with it, and you'll have to make your own rules to keep the balance you need. For example, one of my rules is no weekend flights for business. People are supportive but not necessarily proactive in helping. This might be slowly shifting. That said, if you find and stand by the rules that work for you, it's excellent.