Pros
The people! I can count on every person I work with to do their best, it is wonderful not having to worry about someone else's work. Each team member I have is invested in helping me when I need it. I haven't had to deal with micro-managing like at previous companies. Everyone will help you with your career growth as much as you help yourself with it. It isn't written in stone like at large companies, but some people like clear steps for growth, so it is not for everyone. There is lots of flexibility like working from home, but that also means it is not for someone who is easily distracted. It is best to know who you are and what you can handle. For example, I always did great in college with online classes, but someone who doesn't have the willpower to stay focused wouldn't do to well in this environment. There are also plenty of fun team events, happy hours, and catered lunches. The office is great with a stocked snack pantry and a nice open layout. Also, the variety of startup clients makes for work never getting boring.
Cons
I can't think of any for myself personally.