The two points of gras coming up and mirroring eachother look off a bit, and the hit block is a little too dark I think, the "eyes" aren't quite visible enough.
That's actually a case of tiling not mirroring.
I actually think the tiling is quite good in general. Just on the incline is it TOO obvious I think. I agree about the eyes on the block.
I think the problem with your underground pipe is that the shadows are too dark. Since the environment is supposed to be dark, I would think realistically that every part of the pipe should be at least marginally brighter than the background so one's eyes could distinguish it from the nothingness.
Another minor note, I think the area in shadow on the above-ground pipe is too much.