You will have a much lower standard of living by most monetary measures. Taxes are higher than in the US and regulations/beurocracy is more extensive. Everything is "smaller" from cars, houses, and land to meals. Energy costs - especially transportation costs - are much higher almost everywhere, which forces you to try to keep your energy consumption low compared to how you would live in the US. There is virtually one sport everywhere and its soccer, so facilities/clubs/organizations for any other sport are far behind US standards. For instance, you will not be able to find anything resembling a YMCA where you can workout with weights, play basketball and racketball and go swimming all for some monthly membership. People all live much closer together, so you won't be able to find a place thats even a little "off the grid" this can be good or bad just depends on what you prefer.
On the more positive side, you will have "free" healthcare, but the quality will vary drastically from country to country. In Poland its disastrous for instance whereas in Germany its pretty nice and will cover just about all your health costs and the quality is high as well. France is closer to the Germany side of things but I'd say the overall quality is a bit lower. Also you will rarely if ever work more than 40 hours a week and you'll also get 30 paid vacation days a year from most employers. In Germany, sick days don't count against your vacation days so it all compounds to a pretty big chunk of leisure time. Additionally, there's all kinds of various social welfare programs that will take care of you should you become unemployed or disabled etc. these are extensive and well-funded in Germany and France much less so in Poland.
I'm an expat and have lived/worked in Germany for the past 9 years, basically my entire 20s and working life except for freelance web work I did while getting my undergrad in the US.