Ahhhh Place des Vosges, one of my personal favourites too! To me it's what a square should be in the sense of being a culmination and a destination. Place des Vosges encumpases all that is the Marais. It is a place to go as well as a place to be. Good architecture (although quite specifically historic in this case), human scale, opportunity for various forms of activity (retail and dining around the edges, a museum or two, and lots of space for enjoying the park and the fountains), and lots of foot traffic.
I suppose we can argue which squares are the best or worst, but anybody who's travelled through Europe as an example knows that squares and circles and roundabouts, formal and informal, planned and accidental are everywhere to be found. They are one of the true features of European urban landscapes. I only wish this were a bit more true in North America but due to our ridgid grid patterns only the most planned and formal of squares seems to emerge for the most part. If I could project a desire for distinct urban planning in Toronto, within a North American context at least, it would be for more public square type configurations...bring em on!