Queretaro I found the least interesting one among the Spanish-colonial cities of Central Mexico. It seems quite an affluent city though, probably nice enough to live in. I understand that it has quite a lot of people from Mexico City move there for better living circumstances.
If you're driving around Central Mexico hunting for WHS, Queretaro is a convenient stop and I spent one night here. Did my sightseeing in the afternoon - it took me two hours to find my way around the several tree-lined plazas and look at some churches. The nicest is the Santa Rosa de Viterbo: it has really weird, curved buttresses (see large photo above).
As we're working right now on a Top 50 Missing list on the Forum of this website (for sites that mysteriously haven't made it into the WH list yet), we could also introduce a Top 50 Removals: sites that have made it in when no one from an AB or the WHC seems to have been looking. Queretaro surely would get my vote for that list.