Koshi nage is perhaps the only technique I don't like in Aikido. Reason? When I do it, I can't do it fast enough. I'm really bad at it. Sure, it has improved during my limited time of Aikido practise. But either way, it's damn hard to do... I know that the problem is not the technique, but rather the way I'm doing it.
I'm working on it though. Perhaps it will grow on me in a few years.