Are Italian trains reliable?

Yes — high-speed services are punctual and comfortable, and regional trains are mostly fine if unglamorous. The genuine exception is strikes, which are announced in advance and usually run for a set number of hours with guaranteed services at the edges of the day. Delays on regional lines in the south are more common than in the north. Practical habit: build a buffer of at least three hours between your last train and an international flight, and don't schedule a tight same-day connection between a regional train and a high-speed one you've paid a non-refundable fare for.