<-------- American with US passport who has never been to Paris before.

I'm going from DC to Germany with a 5hr layover in Paris this Sat (4/29). i'm checking in my luggage and my carryon is a backpack.

1) Is it recommended that I sightsee Paris? If so, what to do in ~4hrs?

2) Is it a pain to get back to the airport and thru security?

THX