You'll definitely earn way less, but you'll be entitled to a lot of vacations (5~7 weeks of paid vacations).
The Americans I know that went to work to France don't want to go back
Life -- not work. Working there was a nightmare. The pay is low, and while you can live on it, you're not really saving. For a while I was part of the startup community there and while there are many great programs from the government, there is a bit of a local mafia deciding things. Investors were so unsophisticated that technology itself seemed to scare them.
All-in-all, if I could have made it work, I would have done so in a heartbeat. Living there is simply a small piece of heaven on earth. There's just no way to viably work there that I could find.