Ravintola Sassi is very good http://www.ravintolasassi.fi Italian style food.
The very best is Creek Restaurant http://www.crecian.fi They are nro 1 entreperneau 2008 in Oulu
Very good owners, lovely athmoshire and the food is good!
If no willing to walk that distance try Restaurant Istanbul Oriental http://www.istanbuloriental.fi/
They are not open all day long - but worth to try - allways a hit!
If you like chinese food, try hailong restaurant or beijing restaurant. They both have chinese menu for only chinese people which means those are real chinese food that you can get from china and it is cheaper mostly than a finnish&english menu.