Pros
Food is pretty good. There are definitely some very talented engineers. In several ways, engineering practices are top notch. Work/life balance is good.
Cons
Office politics are extremely pervasive in Square. I've known coworkers fired over personal disagreements. If you don't drink the kool-aid, you're gone. Management refuses to admit mistakes. The communications team seems to focus on placating employees, not telling an inspiring narrative to the rest of the world. Generally, projects move at a glacial pace unless management happens to fancy your project this quarter. The next quarter your headcount could be gone. I saw projects take two years that should have taken 3-6 months. Compensation is unimpressive. I think there's more of an effort recently to improve it, but for many employees like myself it's too little too late. For as many great engineers as there are, there are equally as many really poor engineers. Square grew far too quickly, and its talent suffered as a result. In general, engineering makes little investment in the future. Technical debt is extremely high with no plan on how to pay it down.