1- There is excessive white-space everywhere (like every other modern web-app). I feel like it was designed as a mobile-first solution.
2- There could have been smarter features regarding gamification and karma. Currently you can only hit like button (the total like count of a user is not even visible)
3- If a post has many replies, it only shows them up until a certain point and you have to scroll down to view more. These javascript shenanigans should not exist in a forum app IMO.
I have never used a nimforum-based forum but a quick browse in https://forum.nim-lang.org/ shows that their UI is more dense (less white-space) which addresses point 1 above.