@Ray Borowski - "You can choose what teams you want to appear on the side bar"
I have just tried that and it doesn't work. Despite having a tall, narrow window with plenty of space, I am stuck with Activity, Chat, Teams, Meetings, Files and a "..." menu for the rest (which would easily fit in the remaining space - don't get me started on that one). I can't drag these around, hide them, rename them, or drag new teams into this area.
The notification granularity I would like to see should be customization of what kind of notification I get for each different event, globally, per-channel, and per-person. So I'd like to be notified with a pop-up and sound on the "Important Team News" channel, not be notified at all on the "Gossip" channel, and be notified by taskbar badge only on the "General" channel unless it's Graham because he only ever posts "amusing" gifs, or if it's an explicit @mention, also display a pop-up and a sound. Just a global "all off" and "all on" is not enough.
Compact mode is even worse than private channels. They have been "working on it" for 600+ days, and four separate people in the UserVoice chat (including me) have actually changed the CSS to make it work on the web version. Given that the Electron App is just a web page in a box, it should be nearly-trivial to allow a switch so a different CSS file. The latest attempt (by Emannuel) is by far the most complete, and took him 4 days. How can it take the development team 150x as long? Unless, of course, they are actually not working on it at all.