yea a city needs open spaces, but those open spaces should be in the form of designated parks, rather than green spaces on the side of the footpath (which is a feature common in suburban areas in europe), a city should be dense and compact, the buildings should border the sidewalks so that people can maneuver freely without having to follow the designated grass path - in fact people sooner or later will start walking across the grass, and making the place look untidy (the grass also needs to be maintained, or else it will turn brown).
also, the only way of creating a truly pedestrian space with a cosmopolitan feel is by having shops side by side, buildings side by side etc...; if the buildings and shops are spread out people will not walk, simple as that (thus, creating a deserted-car-dependent city). :S
the only proper city i know that doesn't follow what i described above is Dubai - and well, there's practically no pedestrian life there. for a successful city (pedestrian wise) think london, newyork, paris etc...