...and they apply equally to all channels. I'm in the company "what to get for lunch" channel, but I do not ever want notifications from that channel unless someone specifically mentions me. I don't even want to see there are unread messages in it. Can I configure this? Of course not.
I also don't want to receive any notifications from some bot users. Can I ignore notifications specifically from particular users? Of course not.
And don't get me started on searching. I want a simple incremental search in the current buffer, ideally regex capable. Why does it have to open a god damned sidebar that doesn't even fit in the window to show the results?
Actually, the whole thing about how incredibly inefficiently it uses the screen space it's given is a real bother. I disliked Skype for taking up way too much space, but Slack is even worse!
I realise most of these complaints are about the official client but it's provided as a part of the service and there aren't many alternatives yet, which is a problem with the service.