Here's my feedback based on my experience using it, and using try.discourse.org as a specific case to examine.

- You use 73 vertical pixels after every. single. post. for just the reaction and permalink buttons. My browser's inner height is 947px when maximized, that means if I'm seeing the bottom of 4 posts, a full 30% of screen real estate for reading posts is dedicated to showing those buttons 4 times.

- Similarly, having the username and date sit above rather than beside each post, eats even more vertical space. I'm on the page because I want to read. the. thread., let me!

- If I scroll up too fast from the middle of a thread, I end up pulling down the top navbar, which, once the next set of posts loads, is immediately hidden again leading to the whole page jumping after each upward scroll.

- The first place it puts me is "Latest". I can't speak to the distribution of use-cases, but that's never been a helpful place to put me when I first land in a discourse. If I'm new, I want the lay of the land. And this is more true, the more busy the site is. So dropping me in "Categories" would be much more useful.

- Is the in-page scrollbar on a topic page scrolling through posts or time? Kind of both?

- A pipe dream I think, but I'd really like it if you made the browser think the page was actually the length of the full thread and then when I scroll my browser scrollbar it adheres to my expectations of navigating the page, even though things are only loaded on-demand.

- Once you scroll the topic list, you lose the header, and no longer have a reference for which number is "Replies" and which is "Views". You've got tooltips at least, but it still lends to the overall sense of confusion and not knowing where one is.

- I want to see the name of the original poster of a topic in the list view. No being able to hover to find out is not sufficient because it's not glanceable.

- In the list view, there is no visual distinction between the original poster, frequent posters, and the most recent poster. Original poster as first is fine, but it took me about 30 seconds bouncing around various icons and waiting for the hover to finally figure out that the last one is always the most recent poster. I thought that maybe for really popular threads it was only showing frequent posters.

- It is not sufficiently clear at a glance that, on a post in the list that has both a category and tags that they are separate things for separate ideas. At least bold the category

- You override ctrl-f in topics but DON'T override it in the topic list despite it being the same search. I find it annoying I can't use my normal ctrl-f, but for the behavior to be inconsistent is confusing.

- try.discourse.org in particular has a category "Uncategorized", but there are topics that have no category, not even "Uncategorized". Actually I just noticed that despite being in the "all categories" list and having a color associated with it, topics without a category don't get marked as such neither on the list page, nor the thread page, which I expected since it was treated as one in the navigation. Does the color for "Uncategorized" ever get used elsewhere?

- I expect to be able to search for multiple tags at once using the tags dropdown navigation

I sincerely hope this helps to improve my own experience when using discourse one day, but from what I've seen in investigating this, I suspect the level of minimalism in place is done on purpose, despite the negative impact on discoverability and usability, in which case basically everything I said will be dismissed since it's not what you're aiming for, or at least you don't think it is.