I lived here for a year and a half. It is not characterized as a very touristy city, but you may take a day to wander around the streets downtown, the university and the Bio Bio river. Nightlife is fun, try the TREINTA Y TANTOS empanadas in the Barrio Estacion, they are really good.
If you are planning to travel south of Chile, this is a good place to stop for a night and continue with your journey.