I recently took a trip to Bochum, Germany. They have a light rail system that goes to every small suburb, the university, and is centered at the Bochum city train station where there are cabs, bus lines and connections that get you to any surrounding city.
It is maybe 6-8 lines total and was incredibly useful because it was designed to be, I didnt need a car to get anywhere and it was clean and cheap (2 euros per trip) .
The new Q-line in Detroit is 1 line that is three miles total and is more designed as a tourist trap, most people dont work three miles away from where they live. You need to connect it to other systems like an airport or a bus station, and you need more than 1 line (duh).
If you gave everyone horses and only build a three mile road you wouldn't say that "cars are a failure, and roads lose money". For some reason in the States we build out a tiny one line system and then throw our hands up in the air when nobody rides it.