This could be made to look significantly better with a little effort. Mostly by using stronger black outlines on the characters (such as in comics), not using plain white for the characters' bodies (some simple shading would go a long way), and most of all not using those green criscrossing lines in the background.
Use flat colours for the earth, sky and grass instead of low-res textures, make the blades of grass different heights and thicknesses, make the yellow lightbeam transparent, add blob shadows to characters, and redesign the UFO which is the shittiest looking thing in the image.
Also develop a 16 colour palette for the game and stick to it. The yellow and the blue are really clashing here.
I like the cow image a LOT better than the stars one, because the cow idea is less generic. In short, the cow game would probably be better, but might require some basic art practice on your part. Just study how comics are outlined and shaded, use some transparency, don't use plain white, and use a well defined palette instead of random colours.
Edit; also try working on the proportions of things (cows shouldn't be bigger than UFOs, characters shouldn't be half the screen height in a sidescroller (which this looks like). And try to avoid 90 degree angles on anything except maybe buildings.
Edited by the_cheetah, 31 May 2014 - 09:53 AM.