Thanks for doing that, and thanks to all for the feedback and input so far. For the interface I want to set up, I'd like the ability to enter notmuch search syntax in an input box, and also show tags applied to messages.
The interface presented by the current version of notmuch-web ticks a lot of boxes for me. Speed of being able to enter free-form search syntax (or ideally, selecting from a list of favourite or predefined searches) and returning the results quickly, I think are critical for how I'd like the interface to be used. I see that the DFeed instance has an advanced search facility, but it's a few clicks away.
I've not looked seriously at the other suggestions so far in this thread, though.
Cheers,
-- Matt