To be sorted out into feature requests or bug reports eventually maybe. Consider this a blog post for now, I guess.

I spent a little bit of time checking out Hazordhu in the webclient.

Comparison image: http://i.imgur.com/WfiMxtq.png
The most game-breaking difference is that grids have no mouse interactivity at all (although statpanels do).

Other differences I noticed:

HUDs don't support invisibility?

Movement seems slower and more floaty? It doesn't use key-repeat, so I'm not sure what this could be from.

The text with a border is somehow different:
DS: http://i.imgur.com/FZ5mrXo.png
Web: http://i.imgur.com/brqYDav.png

Text in buttons automatically shrink, but never get bigger again. http://i.imgur.com/sXos8QL.gifv

This little overlay is too high:
DS: http://i.imgur.com/XV8NZlW.png
Web: http://i.imgur.com/LVPbzIt.png