I tend to throw a mix up at my players. I give a basic general description of the architecture or layout, poverty levels, a general feeling of how many stragglers are about...whether or not its a safe area and then I will also elaborate on any truly unique buildings or architecture. Some of these unique buildings are "keyed" but some may have been built for specific reasons (i.e. for a local hero).
Of course, I work in the civil engineering field and am forced day-in and day-out to deal with differing styles of architecture and engineering etc. So, I merely pass my overdosed feelings onto my players...not that they seem to mind
Architecture isn't the only thing that gives cities a feel. A large amount of people can lend a claustrophobic feel to the city. If everyone is dirty and unkempt, it could impose a feeling of hopelessness upon the characters. The first "city" my players arrived in had been assaulted by some bandits...houses had been burned down and townsfolk slain. I constantly made sure they felt the overwhelming odor of charred flesh and singed hair. I made a large effort to make them feel this "shade" of the city because it contrasted with what the city usually is: a peaceful, mainly thatched building city with a freshly built and studiously cleaned keep. Yet the people were being herded about, because they were all distraught over the attacks. They hadn't expected it, they hadn't experienced anything of that magnitude in such a time, that the overwhelming feeling of chaos and loss
was the city at that time. The city wasn't an assemblage of buildings with this type of architecture or that, it was the description of its townsfolk and their emotions.
Anyway...I'm not sure I made much sense...but I hope you can gather any wisdom from my lengthy and seemingly pointless words.
~Fune