Well, my opinion is that Nodebb is an excellent forum, but suffers from some basic flaws. If you use the default, with very few (limited) features, then OK. As soon as you want something more, you realize that Nodebb is not the solution. Also, markdown is simply not for forums (as stated in posts above). Formatting text for the forum software requires more than markdown offers (it is a system for simple text formatting, not for forums).
The main disadvantage is that it is very difficult to itegrate user sessions and integrate application with other applications. Also, bugs that which occur after installing some simple plugin show that the forum is not modular (bad plugin system). And third disadvantage is database (no suppot for MySQL for example for large amounts of data).

Opinions differ. My opinion is that markdown is pretty bad and I don't think it will be the future.
Example of this is that none of the users did not know how to use markdown, but did not have much problem with BBCode (learns pretty fast). If markdown shorter, does not necessarily mean that one is better.
Users simply knows that B is bold, URL is link, IMG is image and just put it between tags and it's harder to mix with raw text than markdown. Also, I remember on old forums (and also new) you have option to create your own bbcodes and insert HTML for tooltips, embed youtube video or any other video, spoilers, text highlight and any other HTML code.
There are many more options and the more flexible. Markdown is designed for simple formatting (bold, headings, lists and a few other small things).
One of the users asked me how to insert clicktable image with Markdown. I show him and he answered me: "Wow, it's scary! How, invented this?" And I totally agree with him.

After all, it does not much matter. I do not see a future in Markdown. Also I think it would be much easier to use BBCode with WYSIWYG editor than Markdown because BBCode structure is logical like HTML structure.

However, I decided to use another forum, because NodeBB is very buggy (see first posts).
Of course, this does not mean that I will not follow its development, but as long as there is a great incompatibility with plugins (after core update or similar) and no integration of user sessions and database, I think that this forum will be limited to a smaller number of users.

Regards.

@jarey, thanks for reply.

I am using the 0.7.0 stable branch.

Seems to new bugs arise every day. Forum is quite unstable.
Now pictures from profiles of some users missing (including my own), without any reason.
One of the user said me one day ago that he can not see the pictures, and now it is happening to me.

And to add - markdown in textarea is in my opinion very ugly. Maybe people who use a wiki like, but most users hate it. WYSIWYG editor is much better solution (even old style bbcode).

Yes, but not a current user data.

Also, I noticed a lot of errors in console like:

WebSocket connection to 'wss://WEBSITE.com/socket.io/?EIO=3&transport=websocket&sid=9OLbJXy-15tQ70WWAAGX' failed: Error during WebSocket handshake: Unexpected response code: 400

templates/activeusers.tpl?v=1433525758000 Failed to load resource: the server responded with a status of 404 (Not Found)

Uncaught Error: Unable to load template: activeusers (Not Found)

[translator] Global invocation of the translator is now deprecated, please require the module instead.

I must first note that this forum is really great, and people love it. Quick Navigation, friendly interface, modern design, looks good on mobile devices, differs from other forums that are still suffering from old style (and slow) navigation etc.
On the other hand I have to make a couple of positive reviews:

Database - although Redis very fast and scalable database, there is a problem when huge amounts of data. Database is excellent for fast applications, caching, analysis (small forums) etc. but I'm not sure what will happen with the memory when huge amounts of data.

I noticed that almost every addon (plugin, theme) is broken. But it's not so terrible.

Why some people avoid this board is that it is impossible to initiate session or to check whether a user is logged. This option has almost every forum and it is a great disadvantage.

With all the positive things that provides this forum, there are some major flaws that "rejects" some users.
Of course, keep up good work.

Regards.