The 3 biggest problems I have with it are search, history, and stability. Scrolling back in time past a few weeks will frequently just crash Teams for me. The search Teams has is beyond basic and genuinely unhelpful most of the time, and I frequently just don't get my alerts despite being available and someone directly @ing me. Then there are tons of small problems like Teams automatically setting me as away if I don't touch my mouse for 15 minutes or sometimes I'll have Teams on a second monitor while working in a primary monitor and Teams will have set me as away for no reason. Also Teams threads are literally the worst UX I have ever had. I am not exaggerating