The Metro system in Lisbon is very user friendly. To begin with, there are only 4 lines with several corresponding stations. You purchase your ticket using vending machines located at the entrance. One can purchase a one way ticket or multiple tickets. There is €.50 charge for a physical ticket so if you want to save money, you can continue to add more money to your existing tickets.
Metro system is clean, fast and reliable. At any station, there are flashing overhead signs that tells you the current time and when your next train is approaching. In most stations, the train stops just a few seconds so one better be ready to jump on or off. The two of us have not experienced traveling during peak hours. So far, no pushing or shoving.
While not at all modern compared to Tokyo or Paris, the metro trains in Lisbon are comfortable, reliable and very inexpensive.
Aloha -- Cathi