Madison Square Park always seems to be hosting interesting art projects; in 2008, I saw Pulse Park there (my writeup and photos here), and last night I checked out Jim Campbell's Scattered Light. The piece is a three dimensional array of LED lamps, across which Campbell has mapped video of people walking:
To see the effect, you have to see it in motion:
The piece is pretty cool, but my gripe is that you can't really get near enough to it to experience it at different scales.
Also, it's kind of reminiscent of Shake Shack nearby: