Icons are not realy good. Let start from the point that they are different. Different in style and in quality. If Reveal is totaly bad then way of the hoe is better but totaly different. The third icon with flag is a great example of bad quality tryes of making good icons. The last is pure CnP and must die.
About first icon - we can start from bad quality of light FX. Try find some tutorials about making FX on ur work. The second part is lost shading geometry. There, where a top cloud should be overlighten or overdarkened (depends of liquidness), there is part darkened and part lighten that is realy unrealistic and looks mess.
The second icon (Way of hoe) has big problem that a object, shown in icon is not a hoe. Also, grey color on BG make icon pale. Try increase contrasts, add juicy color selection. Most problem of ur hoe is not a shape, that make it hard to recognize it as a hoe. Most problem that object head is not shown as some metallic item, try make some realistic light reflection, metallic shadows and etc. Not a plastic, like here.
The third icon has very premetive shadows cuz of wich the object has realy broken shape, i mean that shape of that flag is not a square, but some broken thing.
I mean that if u spread that pattern, u will see it not as a square but as a result from games of childrens with scissors and pattern. The second problem is a spear or whatever holds a flag. Great problem with shadows. I mean its totaly shadeless and reminds me a flower stem. Make it wider and add shadows.
About ultimate - try more and more freehand and show there result.
