It's user interface is unintuitive and messy. I find it difficult to find the context I want.
Search doesn't seem to work.
It takes a long time to load.
When it eventually loads, it pops itself up in front of whatever I've opened and started working on (whilst Teams is busy loading) to take all my keystrokes until I notice the keystrokes aren't showing up in the program I was already using - I've seen at least one person's password entered into a chat session because of Teams "grabbing the front".
And, finally, Teams has taken the initiative to redefine "full screen" such that even that unambiguous terminology is now meaningless. Full screen now means "zoom in, just a little bit". Fuck you Teams.
Screen sharing / video conferencing works fine, however. Except the full screen thing, so even the decent bit has a large caveat.
My apologies for the outburst, but I had to get it off my chest. Teams fucking sucks.