We enjoyed our time in Portland. We were happy to be staying in downtown, as the downtown area is very pretty, with lots of restaurants, great shopping, and a picturesque riverfront walk. There's cruises along the river, and speedboat trips are also available. There is great public transit throughout the city. The downtown core is a "free transportation" zone, and there is frequent tram service to areas outside the downtown area as well.
In the evening, the downtown felt pretty safe. There was many restaurants and cafes still open, and people wandering around everywhere.
Portland is a very family friendly city, with lots of fountains in squares that we saw kids playing in. At night time we were also treated to "flicks on the bricks", which is a giant outdoor cinema in Pioneer Courthouse Square. They were showing Ghostbusters and everyone was having a great time.
Powell's Bookstore was also a fun wander - it's certainly one of the biggest bookstores we've ever been in, but we were disappointed by the lack of chairs or anywhere to sit and read - I guess we've been spoiled by Borders and Barnes and Noble.