Pros
Really excellent brands were among this agency's client portfolio at the time of working there, which meant you could build experience extremely quickly (though were thrown in at the deep end whether or not you seemed 'ready' for it). Most of the team were very lovely people to work with. Professional growth opportunities were there if you sought them out, but rarely were you afforded the time to actually pursue them to their full extent: the initiatives also benefitted Dentsu (parent company), and so you'd like to think you could pursue these initiatives during your working hours, but often you were expected just to add it on top of your existing workload.
Cons
At the time of working here, the way workflows were managed, especially in my department (can't comment for others) were extremely chaotic and led to overworking. Any bonuses were communicated badly (some got them, others didn't, and those that did were beckoned into a room without much thought from senior management, which led to rumours/speculation from colleagues). Pay bands were behind industry standard.