Too difficult to see unread messages
It's very difficult due to subtle font differences to see a read vs unread message from another user. Unread messages are simply Bold and read are standard font.
Lauri Lehman commented
This makes it really hard to see with a quick glance which channels have unread messages. I have to look at the name of each channel carefully to see if they are boldfaced (I am using a dark theme). The settings should have an option to choose a different color for unread messages, for example.