By comprehensive system, I mean a system that (a) covers the entire country; (b) offers an entire spectrum of schedules, from shuttles and locals to premium expresses; and (c) offers an entire spectrum of hard and soft product offerings, from bare bones high density through seated business class to private cabin in sleeper overnight trains.
Virtually all other countries in the free world have 1-2 sleeper trains - Ocean & Canadian (Canada), Indian Pacific & Ghan (Oz), Night Riviera and Caledonian (GB); Lusitania and Galician (Spain); Tucumano and Cordoba (Arg), running anywhere from daily (UK, Spain) to near-weekly (Canada, Argentina). There is also the Thello, Nightjet, and Stockholm boat sleeper. Brazil only has two regional trains and no other offerings. Japan has one night train, maybe two.
Of those countries, Argentina only has a few regional trains that run weekly and one (Mar Platense) with 3x/day. Australia has a decent regional network, and most of the European countries have fine HST and regional operations.
The only countries in the world that truly operate a large and cross-country comprehensive sleeper/regional/HST/corridor/long distance operation are Russia, China, and India.
The new Acela: It's not Aveliable.