It's a "productivity tool" that actively wastes my time. If it _just_ did messaging and conferencing and had reasonable tools and _configuration_ around those options, I might not mind.. it's all the other useless cruft they insist on forcing into the product that never really works properly.
Notifications. Someone put a thumbs up on my message. I get notified twice. Once in the cat and once in "Activity." You can hide "Activity" but that doesn't stop the notification. You can't configure this.
One day teams decided that the window with the view of myself should be mirrored. There's no option to change this. If you're using your camera to show documents or other items, this is an absolute nightmare.
The background video filters work once. If you join a second meeting, they never work again until you restart the browser. You can text chat but you can't video chat with yourself, so there's no good way to test your camera setup until you're going live.
For several months my calendar lost the time column on the left side. I had to open each meeting to see what time it was actually set for. That randomly came back in December.
Twice I've been trying to present something on a call when a dumb "hey check out this new feature" dialog popped up right into the middle of what I was doing. Once it captured the click, and then promptly crashed when it tried to open whatever thing it was hyping. Even if you're just chatting, the pop ups steal focus and interrupt what you are doing.
Once a day teams will start using all the CPU and will stop showing chats or notifications. I have to actively watch the CPU on that machine to see if this is happening and I need a restart. Most often I find out when I get an email that shows me an unread teams message or someone asks why I didn't answer their call.
The UI is garbage and there are zero keyboard shortcuts. It constantly asks me if I want to "replace the attachment" simply because I once uploaded a file with the same name to an entirely different chat.
You can't forward a chat. You literally just have to copy and paste it to a different user. If you join them to an existing personal chat, it just creates a new specific chat for whatever ad hoc group you tried to create.
The whole thing is a poorly thought out also ran set of extensions designed to stave off competition and it's all built on ancient Microsoft Exchange technology. I sincerely hate it.