Zillow can be a great tool to get a ballpark guesstimate of a property's value, but take it with a grain of salt. It works best in tract homes or cookie-cutter communities. It's dubious in areas that have a lot of property diversity & older homes, like is most urban cities.
A fancy algorithm just can not take into account intangible factors that affect value like view, curb appeal, layout, schools, and so forth. I'm just sayin'!