Copy + Paste sucks and isn't consistent. On my machine, if you copy a message, it includes a header, indicating who said it and when. I can't change this behavior in settings, and, infuriatingly, this doesn't happen on other people's machines in my organization.
My biggest complaint is that the screen sharing functionality is broken in surprising and interesting ways. Let me count them. One: I cannot always reliably control another person's machine. Two: When I type on another person's machine, the input is in the controlled machine's keyboard. Three: when I hit a hotkey (ctrl+n in Excel for a new workbook) when I am controlling another person's machine, the hotkey fires twice: once in the controlled application, and once in Teams itself. Again, there is no setting for this. Four: I have at least one person in my organization whose Teams freezes when you try to remotely control his machine.
Lastly, I have Teams on my phone and on my work laptop. Calls ring on both devices. I have no desire to ring on my phone and AFAIK there isn't a setting to force it to ring only on certain devices.