As tourists, we got a Eurail pass, and international travel was as seamless as you could expect (at the time, the Italian trains were slow, the French trains stank, and the British ticketing offices were full of useless queues. The German trains were a little nerve wracking because the conductors were in a blind panic because the train was 30 seconds late).

Anyway, some computer figured out the transfers for us, and the itineraries were fine.

The only real problem was that we had to book weeks ahead. They physically mailed the tickets the US. I can't imagine it works like that now.

Either way, it's proof the patchwork of national operators can work well together.