The Grand Canal is its greatest attraction, but the reason Venice is such a fun city to explore is not the canals but the complete absence of cars — and also of motorcycles, mopeds, bicycles, and scooters, though we did encounter some prams and the occasional wheel-chair — which are relegated to giant parking stations where the causeway to the mainland starts.
The water buses only run up the Grand Canal, around the main island, and to the outer islands, while other than at the regular Grand Canal crossings, where they stand in for bridges, the gondolas and water taxis appear to be used only by tourists. Walking is how one gets around Venice, with the regular bridges over the smaller canals making good photo opportunities but also something of an obstacle to the less mobile. The complete absence of vehicles means the narrow footroads ("calle") and small squares don't seem cramped and cope fine with the volume of pedestrians.
This is of course enabled by the canal system, which allows deliveries of goods and disposal of garbage to be done by boat, with hand-wheeled carts used for "the last fifty metres"; the canal system complements the network of footpaths in much the way the lymph system complements the blood circulation. So ultimately it is the canals which underpin Venice's attraction.