I had one letter from a prof who said he'd mention all sorts of great things about me. I enjoyed his class and got to know him really well over the years. I learned later that his LoR was awful. It wasn't about me at all but about my research. So even though this prof thought he was writing a great LoR, it sucked and I was lucky I got in anywhere. Fortunately, I had had an interview in the process with the Director of Admissions and we had a great convo.