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Yes, I would find it impressive. Problem is, there's about a 5% chance I'd ever get to downloading and running it. Especially since it very likely wouldn't be compiled for mac or linux (the only systems I have) and I very very likely wouldn't feel inclined to compile it myself. That's why we love javascript demos. We're lazy sods.
In which case the impressiveness must be coming from the lack of domain familiarity. It's basically getting excited about a game physics 'Hello World'. I remember a good few years ago a colleague writing a fully textured 3D cloth sim that would remotely unfurl on your screen, displaying a given message on the cloth. He used it to display goatse.cx to me, which I wasn't very pleased about. This was developed in python…
One of the nice things about a site like this is being exposed to domains that one is not familiar with. I for one know beans about physics simulations like this, so it is interesting.
Also, as someone who recalls what Javascript was like 10 or more years ago, yes, I am impressed with what it can do now.