See my reply below about radical changes. Portland did a lot of things right. If you haven't been there it's quite an enjoyable experience. Not just the transit, but the little parks downtown, Powell's books, etc. The transit is cheap. The MAX light rail goes east, west, and north into the suburbs (and would have gone to Vancouver WA if they hadn't voted it down). The east line was the first, unfortunately it has way too many stops. But they built it in open woods in Gresham where they wanted development to occur, rather than letting sprawl happen and then having to take out businesses for it. But many people I know live in southeast Portland which has no MAX, and you have to wait half an hour for a bus on Sundays. This even though it's an inner-city neighborhood close to downtown.
Seattle has a better bus system, more frequent, almost 24 hours to the inner neighborhoods and the airport, and almost as cheap. But it's only buses. So if there's a baseball/football/basketball game or just an everyday accident, you'll be sitting still for a while. They are building light rail, and we almost had a monorail too but it was cancelled. (Not the 60s monorail; I mean one that residents could actually use.) The regional organization that's building the light rail, Sound Transit, refused to consider monorail or PRT because "light rail is the only system proven in the US, so it's the only system we can get a federal grant for". The monorail advocates said screw the federal funding, we'll build it ourselves. It would have covered the west side, where light rail was not slated.
It sounds like you've read Jane Jacobs (The Death and Life of Great American Cities); she was the first New Urbanist if you want to call it that, and has many good ideas about making cities human-scale even though she was writing in the 50s. Basically, things have to be "small". There can be a lot of small things over a large area, but no huge housing developments or lonely big buildings. Chicago... is partway there, but still has more "bigness" than it needs. I think it was Clark Street between Belmont and Fullerton that I felt that, near some big block-long stores. And Fullerton near Orchard Street; things felt a little more spread out and residential than they had to be. (I don't believe in pure residential areas.) I don't know about Chicago parks, but Jacobs points out that parks in general must be laid out for the convenience of the park user, not built arbitrarily to look pretty. So many parks have empty benches... because they're not in places where people want to sit. People want to watch other people, so benches near other people get well used. Plazas get well used for the same reason. Does Chicago have any central plazas? Those are rare in the US, but they're the things that could make the biggest difference in making a city "comfortable" if done right. But they have to be close to people's houses or wherever they would normally be anyway.
Transit suffers from the same problem: you have to start with what the riders want. Speed, frequency, comprehensiveness. Most transit systems fail on all three counts. Cities don't build what transit riders want; they build the minimum necessary to get the advocates to shut up. Or they delude themselves that one light rail line will solve everybody's transit needs.