The Paddan boats are a classic Gothenburg introduction: low, open sightseeing boats that slip through the old moat, under very low bridges, and out toward the harbour. The route gives a quick sense of why the city grew as a trading port rather than just another inland Swedish town.
It is touristy, but in a useful way. Do it early in a visit if the weather is decent, then use the view from the water to choose where you want to walk next.