If you think HTML5 game design is stuck to 2D, probably you did not try PlayCanvas .
PlayCanvas is a visual development platform for 3D web content. Both the tools and the web apps you build are powered by HTML5. The entire software platform is web hosted so there’s nothing to install and you can access your work from any device that runs one of the supported web browsers.
If you played with Unity, you will find the whole workflow very familiar, since you basically import graphic assets, build game entities by placing them directly in the world, script entities when needed then publish the game.
This is your base project PlayCanvas will create once you register and sign in for the first time:
From null to full HTML5 cross platform game
If you don't know where to start, then From null to full HTML5 cross platform game is the book for you.