Really neat, webgl has surprised me at how slow its been adopted.
My impression is that basically all web-based games use WebGL or Canvas these days. Now, most WebGL users are really using something higher-level like Three.js or Unity. But I don't see it being under-utilized for its intended purpose.
I'll tell you this though: creating your own engine makes you appreciate a lot more games and well established engines, with that ridiculous realistic graphics.