Pros
R&D department is run well, relatively small/agile teams with lots of autonomy. Good technology, smart engineers, nice office, good compensation. Human element/social dynamic is healthy -- people are mostly working on projects they find interesting, people are relatively transparent vis-a-vis hierachy. Not too much politics.
Cons
There are parts of the org that are still the wild west (relic of startup culture) but mostly it's a big team now and lots of $ on the line, so the typical challenges of balancing stability with innovation. Some engineers will be frustrated by the Process which is mostly well-intentioned but occasionally rigid. Nobody has ever heard of Criteo outside Paris. Sometimes hard to stomach the company's mission -- when you explain what you do to people the reaction is often negative.