I have used various forum software since the late-2000s (SMF, myBB, phpBB, vBulletin, IP.Board) and the Discourse UX is very different from all of them.
The notion of organizing threads via category rather than forum/subforum is alien to me, I prefer a more rigid and navigable hierarchy. The “Discourse way” of navigation seems to be filtering by category/subcategory or tag, and then browsing or searching from there. This seems like it works fine but I’m not used to it yet.
Typing a reply to a thread causes a notification to appear which advertises to anyone viewing the thread that I am actively composing a reply. This is invasive and I would prefer to compose replies in a more private setting.
The “Reply” button does schizophrenic things - on every other forum, “Reply” is called “Quote” and it puts your post inside my post. On Discourse, “Reply” puts my post underneath your post (and your post above my post) inside drop-down menus which completely breaks the chronological flow of the thread. Plus it seems the only way to get a quote is to click+drag and highlight what you wrote before I click “Reply”.
The Chat feature is superfluous and is one of the things I disable straight away.
Like counts, view counts, link click counts, and edit counts/edit revisions being visible by default are all also annoying. I am used to individual forums possibly having one or two of these enabled as an opt-in, but seeing all of them all the time on every Discourse forum is weird.
The general layout of Discourse is also bad. It looks more like Gmail than anything else. There is far too much wasted whitespace. Information density is very low. The page width is not wide enough. We may be able to correct this with a theme.
The dual-pane editor is okay but the fact that it floats on a layer above the thread rather than being anchored to the bottom (or below the post I am replying to) is annoying and in-your-face. I will admit it comes in handy if I want to browse the forum and compose a reply at the same time. Markdown formatting is also nice.
Stats/like counts/badges/gamification on user profiles is annoying. Granted the old-school forums had things sort of like this with titles and ranks and whatnot, but on Discourse they’re all modernized and weirdly prominent.
A huge issue I have are the goddamn pictograms everywhere. I wish every button with an icon was either a textual button, or had an icon and text.
I hate this:

And this:

And these:

They should all look like this:

So I can understand what the buttons do without deciphering hieroglyphics.
Despite this, Discourse is still fundamentally something I love: a web forum. I cherish forums and most of these issues can probably be corrected either with server-side themes or client-side userscripts/CSS edits, so part of making a comfy home for myself on this forum will be finding ways to sand down the rough edges.
I will happily learn to love Discourse for two main reasons:
- Maintenance burden for admins is likely to be quite low while interoperability with other software is likely to be quite high
- It is a traditional forum with threads and posts, where all posts are equal and bumped threads immediately appear at the top of the forum. This as opposed to a post/comment model with upvotes/downvotes where only recently-upvoted posts are visible and commenting is inherently adversarial. No thanks!!