Flat cities with a rigid grid are kinda boring and often downright depressing (standing on a street in some of Chicago's neighborhoods, with ticky-tacky little houses marching uninterrupted into the distance as far as you can see, is a soul-sucking experience)...

Limited horizons and change make things interesting. You don't want complete chaos, because things also have to "make sense" to some degree (so complete randomness, like a stereotypical suburban cul-de-sac maze, tends to be bad), but variation is a good thing.

[A nice city to look at for interesting approaches to urban structure which are both somewhat regular, but more interesting that a grid, is Edinburgh, which has seen successive waves of fairly successful urban renewal over centuries, resulting in one of the most beautiful and fascinating cities in Europe. In the "new" parts (150-250 years old as opposed to the older and more organic medieval parts), Edinburgh streets have such features as small localized grids, sized as to with care to avoid large-scale monotony, occasional "circuses" acting as focal points, streets in gentle arcs which are practical for transportation, and yet maintain a constantly evolving street view and horizon, terraces along the sides of parks, etc.]