The log of wood has texture, but no lighting. You can see depth on it's surface, but you can't recognize a light source or some shadows on it.
Also the log could've been a little less uniform/straight
The grass tile should not have such a dark outline. As it is tilable, it must tile seamlessly. If you wish to have a grid on it, you need to keep only 2 of the lines.
Also, an isometric tile can not work out like that on a grid system. You should modify your tile to fit in a 30*16 image (instead of the 34*17 you have now). This will result in a left and right end that is 2 pixels high.
