Lots of cities have nice areas around downtown, but few have nice areas around downtown where you can do everything you need (walk to work, walk to the grocery, etc). They do exist, obviously, and some people are more tolerant about walking through a few bad blocks on the way to work than others, but it is my observation that most U.S. cities don't do a good job of making downtown a desirable place to live. Many U.S. downtowns essentially shutdown after 5pm as all of the restaurants close for the day and everyone commutes back to the 'burbs.
That's the traditional "business district" style downtown, yeah, but afaict there's been a shift away from that in the past 15-20 years, and now many people commute to downtown in the evenings, because that's where all the restaurants/bars/clubs/theaters are. That's definitely the case in the Bay Area, where SF is much more lively after 5pm than most of the Valley is (Santa Clara is basically dead once office workers go home). Was also the case in Midtown Atlanta when I lived there a few years ago; big influx from the suburbs in the evenings, esp on weekends.
SOMA too for the most part. Sadly the walk between workable parts (SOMA/FiDi) and livable parts has goes through areas that are less than ideal for walking (in terms of feeling safe).
