Vantaggi
AKQA is a great line-item for your resumé. You'll work with excellent talent, and will (likely) get to work on some exciting things.
Svantaggi
A lot of changes in the organization lead to a tangible decline following its acquisition by WPP. The "spark" that comes with a talented and exciting independent agency was noticeably lost – it began functioning more and more as a cog in a machine, leading to a lot of talented leadership leaving behind the Founder, as well as the loss of valuable clients.
Limited transparency in career roadmaps and growth opportunities. Low pay considering the size of the organization (and its clients), no transparency regarding pay increase/bonus (if you get one at all).
All things considered, if you're thinking about joining AKQA, I would (currently) approach it as a stepping stone in your career rather than a long-term home.