Lots of weird polish issues in my opinion... One that really peeved me was (for a while at least) you could search for a message, but there was no way to jump to that message from the search results. So you couldn't read the context unless you scroll all the way back up.

But primarily it's that the mechanics are different from things like Slack and Discord in ways that are just less intuitive.

Channels function more like announcements + comments rather than a chat—you are really shoehorned into posting a "Topic" and discussing it in the replies. There's no way to carry a linear conversation in a channel otherwise. And to load replies you have to keep clicking "see more" as if this is a social media site, so it's very annoying when your 800+ comment critical discussion happens there. Not to mention notification settings aren't granular enough, so you either get hammered by all activity, or remain oblivious to discussions which may have popped up in an older Post.

What tends to happen in my experience is small working groups spawn off a group chats because the flow is better for daily conversation there than in Channels. Which, of course hides this activity from anyone not in the chat. And group chat's are entirely linear in Teams—you don't have threads the way you do in Slack, so chat history tends to get messy quick.

The channel-then-thread organization Slack uses is much more natural for the teams I tend to work on, because you just have the one main discussion which can be segmented into threads as needed.

It is a nightmare for us consults that is added as guest so we can join the calls and groups.. You need to jump between tenants and many have problems with seeing stuff or even be able to join a group. The preview is a bit better, I still need to jump between my customers tenants but now I at least get a notification if they write to me (have missed so many calls and messages...)

Edit: spelling

I find it disorganized, poorly designed and buggy.

To test your quality, you need to make a test call, where it dials, rings, and connects. Then it plays a little message and you record after the beep, then it plays it back. For every other program I've used, you hit test, talk, then it plays it back. The Teams methods takes at least three times longer, incredibly annoying when trouble shooting.

If you start a test call, and hang up before it connects, it will ring on your computer forever.

There's a keypad where you dial numbers. When you connect and need to press numbers in an automated menu, you can't use that key pad. There's a different keypad behind a pop-up menu.

Some companies use letters in their phone numbers, like 1-800-AWESOME. It doesn't sort that out for you. If you type letters it tries to call then immediately hangs up without explanation.

These are all pretty small things, but there's already better things out there that don't have these problems. It's also almost unbelievable that it's like this. Teams is at least version 3 of MS's foray into telecommunications software, and it's developed by a team of career professionals. It's absurd that it's so unpolished.