Using WebRTC datachannels for p2p networking in games is challenging and fun.

I am personally using it for networking in a WebVR side project (which is far from finished), where the challenges are the differences between clocks, interpolating between received positions, and more. You can try the current version here http://guido.io/WebMetaverse/ (open it multiple browsers and observe).

I ended up implementing a signalling server (in Elixir) and client, which made me understand much more of what is going on under the hood.