The trains in and to Paris are great! We took Eurostar from London to Paris. It was a very pleasant journey. The chunnel itself, is a 20 minute non-event (just a tunnel). The train is smooth and FAST. While running parallel to a motorway in France it was clear we were going much, much faster than them.
In Paris the subway, the Metro, is the best subway I have been on. The most we ever had to wait for a train was 6min. And it only cost €1.11 per ride.
The Metro is many times better than the London tube. 5 full days riding the Metro all about town, and not a single “signal failure.” (I’ll have to save most of my gripes about the tube for another post)