I stumbled upon Mio Sushi several years ago on NW Johnson and have made it a must-stop every time a visit Portland since. The atmosphere is cozy and unique in a little house in a residential neighborhood. Prices are excellent (sushi is spendy where I live) and staff is friendly. You are greeted by both the chefs and servers when you enter the restaurant and thanked when you leave.
The sushi is presented well and the menu has a large selection of traditional rolls. I understand that Mio has opened several more locations in western Oregon due to their success, but the quality at the NW Johnson location has not changed. Highly recommended.