Using the depth buffer to sort tiles in opengl (objective c/ios)

So I've made a breakthrough in my custom tile engine... previously I was pathalogically quicksorting the draw order of hundreds of onscreen tiles. I managed to do figure out how to NOT do that, and use the depth buffer instead. Here's what I did to save others from pain in the ass research, trial, and error.

First i set the GLKView drawable depth format:

    GLKView *view = (GLKView *)self.view;
    ...
    view.drawableDepthFormat = GLKViewDrawableDepthFormat24;

Prior to drawing anything, we clear the screen setting the bit for depth:

    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

Then, for all map layers that have depth (eg. sprite layer), I enable depth testing, and set the depth function to GL_LEQUAL:

            glEnable( GL_DEPTH_TEST );
            glDepthFunc(GL_LEQUAL);

For layers that don't have depth (eg. floor), disable depth testing:

            glDisable( GL_DEPTH_TEST );

Then in my fragment shader, I avoid rendering pixels which are less than 0.5 transparent:

void main(void) {
    lowp vec4 tex = texture2D ( Texture, TexCoordOut );
    if ( tex.a <= 0.5) {
       discard;
    }

   gl_FragColor =  tex;
}

Finally, when sending vertices describing my triangle strips, I use a vector with 3 elements:

    GLKVector3 geometryVertex;

I set the .z value of the vertex to the 'depth' of my particular tile. Farther away tiles I assign less value; closer in tiles, I assign high values. The tiles closer in properly occlude the tiles farther away; thanks to the vertex shader we don't allow transparent pixels to occlude non transparent pixels (we simply don't draw them).

Pictures

Better looking grass!

I've been working hard to try and create grass that the sprite looks like he's actually wading through:

What makes this possible is that the blades of grass are individual tiles, and that the player's sprite is drawn ontop or behind the grass sprites based on the y position. 

Screenshot