Biggest sacrifices: Pay is kind of a huge one. There are very few companies (even global ones) that pay the same in Europe as they do in the US. If I moved back to the US with my current company, I would get a ~70k/year increase in salary. Social situation is the other big one. It's hard to ever feel like you totally fit in as an expat.
Biggest gains: Quality of life is generally higher - food is better (quality, not taste, Munich's food scene kind of sucks), public transportation is better, healthcare is largely better (although again, a little weird in Germany). 6 weeks of vacation as a baseline in most places and unlimited sick leave. Generally more of an emphasis on work/life balance and taking time for yourself.