Avantages
This is the best fit of both culture and employee competence that I've ever worked at. To give an idea of how protective they are of their culture, I had four rounds of interviews, and only one of them was technical. You could be the smartest person on earth but if you give a hint that you might not play nice with others, it isn't going to work out. As a result, almost everybody I've worked with has been nothing short of helpful and highly intelligent. This company also has numerous employee perks that most companies don't offer such as free lunches every day, a kitchen stocked to the hilt with snacks, and a happy hour on Friday afternoons. This company feels the best way to make money is to staff with top talent, and do what they can to nurture that talent.
Inconvénients
The only cons I've come across are run of the mill issues that you would face at any company. Occasional scope creep attempts from the business side, and they are probably a little more helter skelter than some other companies at the requirements phase.