Having moved from Portland (where it was easy to live without a car) to Minneapolis (where it requires more ingenuity and stamina than I have), I can offer a few comments.
What makes Portland easy to get around in is excellent coordination of the transit system. The main routes have frequent service seven days a week, and the transfer points are set up so that you rarely have to wait long for your next bus. When I went back this past spring, I found that they have developed a smartphone app for finding out how long your wait is at any given stop. The stops are all numbered, and you just enter the number of the stop in the app, and it tells you when the next three buses should show up, not according to schedule but according to their current location. In addition, the transit planners there seem to have asked the question, "How can we make it easy to get around without a car?" as they plan new routes and upgrades.
On the other hand, the Twin Cities seem to have asked the question, "How can we get people to work and back?" If you work in either downtown Minneapolis or downtown St. Paul or a couple of other concentrations of commercial buildings, the system works well. If you're trying to do anything else, especially at night or on weekends, the system fails. The map of the system shows a regular spaghetti tangle of bus lines, one light rail line between the Mall of America to the airport and downtown, one line under construction between the two downtowns, and a commuter rail line that seems to have been placed where few people will ever ride it.
From what I've seen while living here, they just slap lines down on top of all the others without regard to how they coordinate with the system as a whole. The result is that while the system map shows that you can get from Point A to Point C by transferring at Point B, in reality, the wait at Point B would be 30 to 60 minutes.
It's not quite that bad to go from my apartment to the airport, but its unnecessarily awkward. The route that goes past my apartment is one of the better ones in a mediocre system, but taking the light rail to the airport requires first going downtown and then transferring to the train. The price is right ($2.25), but it doesn't work if my flight is too early in the morning.
The best transit I've ever seen is in Tokyo--and Japan in general. The trains go nearly everywhere with frequent service, and the buses do the rest. Frankly, I don't know why anyone in Tokyo owns a car except for reasons of mindless consumerism.