Pros
Huge network of people. Amazing opportunities in Europe. Pick you division correctly as there is a big difference between Siemens Energy, Healthineers and Mobility. Some thrive in North America like Healthineers while others don't like Energy.
Cons
Financial issues in the Energy division has led to a lot of layoffs and restructuring. It is very similar to what happened to GE recently. Lots of discretion is giving to your manager, so under-performers stay if they are close to their boss while the opposite is unfortunately true as well. Such a large company that unless you did an internship rotation, the on-boarding typically is near nothing and you won't learn about the rest of the company without lots of pain. Siemens does a poor job of informing you. Yammer is just verbal diarrhea.