Your work shows us that you're very talented with your rendering, but I'd try to push yourself a little further and include, like others have mentioned, some of the sharp back lighting you see in the original. The way green and blue have been used really is a testement to how brilliant those old pixel arteests were with limited palettes. I'd also suggest following a similar path with your stones lighting.

 

I also find it strange how you've included black shading on only one of the bushes. I'd either use it everywhere (for a really sharp look) or not at all.

The texture of the trees doesn't seem to match the shading quality of the stones and grass either. I don't know what it is, but you might want to take a look at some wood texturing tuts or examples. By the sounds of it Lawrence is the man to ask if you're after pixel examples!

 

I like what you've done with the grass so far, and like I said, theres some nice rendering here! Just address the couple of things I mentioned and I reckon you'll have a stella scenic piece.