Im not going to say that I know exacly what Adarias mean, but I think he could mean that it doesnt tile that well - It looks like several tiles instead of one big. You dont want a pattern that reveals it self and take attention, then you will see its tiled - this is my limited experience.

Also, my limited experience think that: if you manage to place the pixels so they dont start or end at the same horizontal or vertical line it looks random enough, the worst thing for me was when I got two straws at the same length or width - I think its better to have them an uneven number if you really have to have them.

Ill try to demonstrate with a picture soon.

edit:

(tile it up even bigger for it to really show)
There is a noticable pattern going on up in the tile, while there are other problems for me this is the biggest. But if you made all the grass tangenting and such it wouldnt be noticable - so its more or less about contrast(not in color, but in shape and placement) You dont want any eye-catchet. with your latest there isnt any of these since its from the same straws - but as mentioned by Adarias, theyre working in groups of and not as a whole, lose the value contrast or try to remove the outlines. Just my experience - and it doesnt really have to do anything with your current grass tile, but something you could have in mind and experiment with ourself.