I fully agree, the silence (I wasn't always in the thick of the demonstration, at some point Hugo and I cut across to gain ground, finding ourselves in a quiet street), a better view of the things around, and the widening of the streets are the three first things that come to mind.

And it's not just that, but also the fact that you walk right in the middle of the street, and this really contributes to the feeling that the streets belong to you. It makes cities look so much more beautiful.