I assume we're talking about SAFE cities when we want them not to be boring. I find physical layout important. If there is no place for an individual to safely get away from the crowd and "hide" while outdoors, that place is boring. Alleys, micro-parks, gazebo-type shelters, open side and rear commercial yards, old buildings with empty floors, etc., make things interesting...SAFE then depends on the age structure of the community, the national and local economy, and other factors.
I find the newer parts of Las Vegas to be intensely boring by this standard, where you have to get to your room to ever be alone.