That site looks nice - clean, modern and simple. The stones appear aliased and there seems to be some graphical ugliness during a resize although it does go away once the resize has finished. Mostly, I like it from a visual perspective.

Mouse interaction is adequate. You can't navigate with the scroll wheel but one could argue that overloading the scroll wheel in a browser is a bad idea, anyway, so this might not count as a missing feature. Keyboard interaction is implemented - arrow keys can be used to navigate through the moves.

You cannot place stones after navigating backwards unless you return to the head of the current branch. This is a big flaw that should be rectified.

I clicked about a bit and the only domain related bug I could find is the omission of the ko-rule. (Ok, that might be rather a large one, to be sure.)

The HTML looks clean - I approve of the use of a canvas instead of positioned elements. I'd like to hear the developer's argument for using four overlaid ones but it seems plausible that there is a good reason behind this decision.

The Javascript is minified so I didn't review it. I wonder whether the original script was factored into separate scripts for the board implementation and communication with the server-side API?

I did not experiment with the other features such as downloading the game or grabbing a link to the board with its position.

Would you be kind enough to share your materials with others? I mean your presentation looks really good. Though I also teach go to beginners and hunt new players, I'm not graphically skilled enough to make something so good or eye catching. I would consider it great help, if everyone could use your materials for good.