I see a lot of negative comments on this lens, but have not found anything to dislike about it. Perhaps it is because I used it as my portrait lens for my Rebel. If the corners were not sharp, that was a feature and not a bug. The background was blurry anyway from my choosing f/1.4 or f/2. Maybe if the center is not hypersharp, I could have taken that as making the portrait a bit more flattering. Since I have been shooting full frame, I have not had much occasion to use it. I was shooting a small group in a relatively low light setting, so I chose that lens. In retrospect, I could have stopped down slightly more, as one teen as standing slight farther back and was not quite as sharp as the others. But I see that more as a problem with the user rather than the lens.The old 50 1.4 was one of Canon's 'misses', hopefully, if we se an RF replacement, they can make it a 'hit' this time round.
So what is so bad about that lens? I’m curious, not that the answer will make me use it any more or even less.