A lot of icons are copies of the game's box art or some high-res image, which I really don't like at all. The whole point of an icon is to be instantly recognizable, it should be the logo for your game. When you stick this high-res icons next to each other you can't tell them apart!
[1,1] 4/10: What is it? A crude tank? Where are the flames coming from? I don't like the high contrast colours.
[1,2] 1/10: I have even less of an idea what this thing is. Even squinting at it doesn't reveal anything. It's too dark.
[1,3] 6/10: Nice clean image and good colours. It's a bit too detailed for an icon, when regular size it will be hard to tell what it is or read the text.
[2,1] 5/10: The orange is a bit harsh but at least we can tell what this game is about.
[2,2] 7/10: This one caught my eye first, it's very crisp and clear, plus monsters with big teeth are a good way to get people's attention.
[2,3] 0/10: The worst of the lot. I have no idea what is going on here, there is far too much in the image, if I look closely I can see a cow.
[3,1] 3/10: This one doesn't stand out very well.
[3,2] 6/10: Looks like a rabbit in a flight mask. Now I see the background is red and white, that should be changed to colours that are different to the mask thing. The mask is quite interesting and there's nothing else to distract your attention (apart from the background) so that helps.
[3,3] 2/10: Not a good icon, it looks like part of a bigger image, the shark's colour is too similar to the backdrop and nothing fills the image so when this is regular icon size you wont be able to see much.
[4,1] 6/10: I don't like how the backdrop is brighter than the aeroplane. Apart from that it's okay.
[4,2] 8/10: This is the best icon of the lot. It's very clean and clear and the little character is so distinct that you could put up 100 icons and I'd still easily be able to find him (which is what some people's desktops are like
).
[4,3] 4/10: Looks more like a poster than an icon.
Everything worthwhile requires effort.
