The single clearest test of whether a city is a great city is how far you can walk from your hotel without getting bored. Half an hour is our standard. If you can walk for 30 minutes in any direction from a central hotel and still see interesting things every block, the city is great. If you hit a dead zone within five minutes, the city is badly planned or you are in the wrong neighborhood — usually both.
Venice passes the Walking City Test everywhere. Paris does within the Périphérique. Barcelona does in Ciutat Vella and most of L'Eixample. Tokyo does almost absurdly well — its density of small, interesting shops is unmatched anywhere.
Cities that fail the test: Los Angeles, almost anywhere. Houston, anywhere. Dubai outside a few walkable pockets. Most American cities, if you are honest about it — the ones with walkable downtowns (Boston, San Francisco, New York) are the exceptions that prove the rule.
The implication for travelers is simple: prioritize dense, walkable historic centers over central business districts. A bad hotel in a great neighborhood beats a great hotel in a bad one, every single time.