Would you take a little criticism? Or basically just some suggestions. I know you just did it for fun but hey why not.
There's nothing particularly wrong with the trees, I think they look great, but I wish the smaller trees matched the big one a bit better. It gets really dark near the bottom but the other trees stay light. It doesn't have dithering on top and has it at the bottom, but the small trees are kind of the opposite of that.
I think the green bush thing is a little too chaotic to be easily recognizable. Looks a bit like some kind of tiny alien creature to me, leading the advance of a horde of other tiny alien creatures. Sometimes round Zelda style bushes are ok, I think they would fit fine with your style.
I love the effect of using bigger pixel chunks to stipple the edges of grass and dirt, but I don't know if there's enough of it going on. The diagonals are a bit too regular for me (though I know you might do it that way to save on tiles).
And I think the water effect is a little too regular and square in places, looks a bit odd. Almost like it was larger and you squished it down by resizing it with a selector tool.
I made this to illustrate.
There are two slightly unique 16x16 tiles that will still tile next to each other perfectly on all four sides, just to break up the visible grid a bit. I just tiled them like a checkerboard.