Pros
Potential to tap massive research budgets. If you have a great director and project leader, you can make great progress and have an awesome time. A lot of researchers have had the best years of their lives at the Max Planck Institutes. The cost of living in Germany can be relatively low; postdoc stipends are reasonable. Quality of life in Germany is quite high for people with low incomes and it is a great place to be young and single even if you don't speak German. Easy to develop a large international network.
Cons
Even within the same institute, your experience can differ enormously based on your director and project leader, from a fantasy land to personal hell. You'll need to build some contacts to learn the real scoop. Do a lot of homework beforehand and have Plan B ready if you enter an unworkable situation. No professionalism; typical academic workplace problems turned up to 10. If your work doesn't have support, you work out the remainder of your contract writing up old results and looking for your next job. Everyone gets the same net pay but Germans get paid benefits (health insurance, vacations, retirement, seniority pay raises, unemployment benefit) while foreigners get none and have to buy their health insurance out of their net salary. Ask for a contract instead of a stipend, don't accept any bunk about foreigners having no use for the German social security system. You probably won't get a contract as this doubles your cost to the institute. Postdocs cost exactly twice as much as graduate students so the expectation is that you will work at least twice as hard. Think about that.