Great transit system, really busy, works well. But a muted at pass when you land at the airport. It is the simplest way to go if you are in Paris a few days. If your smartphone has an App Store, see if they have an offline metro app that plans your route. This is an absolute must as it becomes really easy to get around. We bought a 4 day zone 1 to 5 pass and had no issues at all. A word of warning - my wallet was stolen on a very busy train that was crowded and this was ally an inconvenience, so don't carrY stuff in pockets, rather a inner zip pocket in a backpack or sling bag and keep the bag in front of you in a crowd!