Why do you need to see where you failed? I do see that when I DO fail. If I do a stream and I see that I fail it, then I know that I failed there. Nothing for me to watch over and over, again and again. If I miss a note or a jump then I do see it straight away since it was me who was playing the map and I do notice where I fail. What would be pretty "nice" is if you could not just watch a replay but also "edit" it, like watch in slowmotion or just a simple pause or even save it to local disk like a normal finished replay because that would maybe help you see what you really did wrong and analyze it. Although I don't know if it is really that easy to do (with the "edit" feature, since the replay in Osu! is not just a video recorded like with Fraps of how you played because there are some cases out there where the replays fail while you didn't actually fail when you did it by yourself. So maybe that kind of feature would make the replay "worse" or even "broken" or simply false. Which will cause more trouble rather than use.