Pros
The best parts are: they are a young collective, some fun outings, fully paid team buildings and a eating/fun area equipped with a darts game, foosball, TV and audio system. There isn't a lot of overtime anymore and working week-end are extremely rare, maybe happened twice in my 4+ years there.
Cons
They have only one major client which dictates the terms of the collaboration. Most of the projects aren't inspiring and for those that could be you aren't offered the chance to do a good enough job. Projects come in bulk, the management does not care a whole lot about quality. For the major client (a WPP company) you have NDAs and you're not allowed to show the work you've for them. Any other clients are treated as B tire clients and their projects are always on the backburner.