Gumbys Hideout

[Vipershark]

The thing that bothers me most is that on the top image, the grass needs a LOT more contrast between shades.
There are like 5 shades there, but it only looks like about two or three because they all blend into one.

edit- and the propellors on the back of the blimp are way too jaggy
add some AA to the outlines so they don't stick out from the background so much.

edit again- and the problem with the satellite dish is that you dithered as 1up (SGB) said above, you should never dither unless you have color limits or are trying to add texture. Satellite dishes are usually smooth, so just use a couple of different shades and get rid of the dithering.