Subtlety of emotion is better conveyed by text than by abstract textual representations of exaggerated facial expressions.
In any case, I think o.o and o___o are pretty well covered by
(that is, there is no meaning or emotion specific to either of them not covered by
), and *headdesk* and *facepalm* are covered by
.
As is, we've got five degrees of simple happiness, two for happiness with eyes closed, two of implications of something, two degrees of "cool" happiness, three simple tongue-sticking-out smileys, two for craziness, three for surprise, two for puzzlement, one for shocked surprise, one for embarrassment, two for frustration, two sad faces, a discontented face, an exasperated one, a depressed one, a sick one, an angry one, and a heart, then an array of Nifflas game characters.
Pretty much everything is covered, and that which isn't can be conveyed by a combination of context and emoticons if necessary.