QQ's emoticons (the 70-or-so yellow base set plus a few others) are indeed incredible. Somehow, for every single feeling you want to convey at any time of the day, you will find one and exactly one matching icon. It's like they created a perfect bijection. And they did this while keeping the icons perfectly readable on small low-resolution screens, and with animation frames you can count on one hand. I have no idea who the original artists are but they have my eternal respect.
The drop in emoticon quality was the second worst thing with going back to Skype (which I have to use because everyone else here in the US does).
The reason that the emoticons are so well targeted is not for the users themselves. If someone includes one of the emoticons, it makes machine-identification of sentiment trivial (compared to reading and interpreting the text).
(not sure whether this is something that everyone knows already : Perhaps I only just got the news... (Presuming this is actually true, of course))
I use :/ a lot in wechat because I don't consider any of the faces to match. Also, there are a few faces where the feeling is right but I don't use them because the pink cheeks (and, in one case, eyelashes) make them seem female-only. It'd be nice to have male equivalents.
The drop in emoticon quality was the second worst thing with going back to Skype (which I have to use because everyone else here in the US does).