I was really excited for this when it came out (because I had used it on android messaging apps before (go messages, if I remember correctly), but Apple's implementation is awful. Also as soon as you pull it away, or go away from it, it deletes your entire text. I'd like the message to save as a "draft" in iMessage. If anything comes up, and you have to leave the quick reply, then you're screwed. It creates so much incentive not to use it.
This is aside from all the other general bugs relating to it.