I like the summer the best, but also like about the winter being wet and cold, because it keeps me sharp and awake to think through my ideas and plans for the future.
Portland is a very "quirky" city. First off, there is no sales tax, so this would likely be a dream place for shoppers.
My wife was upset that she bought clothes in Seattle and then realized she could have gotten much more during our stay in Portland. Portland has a huge issue with homelessness. It is impossible to walk around the city and not see people - both young and older - hanging out on the streets. It would also not be the best place to go for people who are not comfortable around heavily tatooed and pierced people, as that is very prevalent in the city as well. Portland has the potential to be a great city to visit, but when you have to constantly deal with beggars asking for money and witness homeless people bathing in local fountains, it loses some of its appeal.
Its called the "City of Roses, but there are flowers of every kind. The best way to see Portland is by car.
Get a map and have a list of your favorite things to do and see. There is a lot of rain in the winter, but in the summer it is very nice, and there is lots of fruit in the nearby valleys.