Although intuitive, the overall interface (both the physical machine and the on-screen interface) are pretty unfriendly and unattractive. The boring color scheme and text-heavy buttons do not condone careful reading of the buttons themselves which could cause someone to make a mistake in their haste. At best, it causes annoyance when one actually has to read into the different options.
The fact that the session times out so fast is definitely not ideal for anybody who does not have their payment ready right away. Furthermore, it would be nice if the user did not have to restart the entire process if that happened.
The entire system of buying fares might need a complete redesign because the fact that you cannot catch a train that is 2 minutes away because you need to refill a card does not sit well with most users.