These look awesome; you got a lot of detail into these small faces.
The only problem I see is that they don't read very fast at 1x zoom. It may be that they're a bit dark or are supposed to be viewed at 2x, but the expressions don't jump out at me very quickly. At 2x they read a bit better, but some are dark enough that I really have to look at them to decipher what emoticon they represent. The lighter ones read much more quickly; there are just a couple of sets that have the problem. The embarrased expression doesn't read very well on any of the sets; a darker or more saturant blush might help that. Emoticons need to be exaggerated so that they can be very clearly viewed.
Also, the cyclopses seem to be having trouble winking, and the green cyclops must get a lot of water in his mouth when he cries ;-)