
Fear.
Personally I have some very strange fears. Spiderwebs; my greatest.
Another is being abandoned; I think this is a bit more universal fear. Here I have one individual unique square standing alone in the middle of the empty space. With the other two blocks I tried to create some perspective and illustrate distance between the objects.

Despair is the lowest low. Left is generally viewed more negatively than the right. Small in size denotes frailty, isolation, and unimportance, all feelings that can lead to despair.

Joy. I started by trying to make a cross with my three squares but got about this far and thought “BUTTONS!!!”, and what isn’t great about little shiny buttons?
Excitement.
It’s kinda like a square bursting forth with corners.

Frustration. (Like I’m feeling trying to get this image to format right.) Getting things to work, fit. Frustrating tasks.
Alternate: 
Supposed to be fists pounding a third block down, off canvas. Turned out a bit too sad looking to use.
Anger.
It’s really hard to show emotions without visualizing facial expressions, since thats the dominate way we express our emotions. “I packed your Angry Eyes!”
I associate the expression of anger with throwing and breaking things.

