Very nicely done, but there are a few minor things I would fix.
Firstly the all to common error with the diagonal north walls. You probably can't spot the tiles in my screenshot but there is a slightly different pair of tiles that go into these diagonal walls that give a long diagonal wall a smoother look (you might see it if you look really close at
my screenshot, look slightly left from the waterfall and you'll see it).
Second would be the stairs. The tiles you used are made for expanding staircases, and have no borders around them, so they don't look quite right.
Third is watch your copy/pasting. I noticed a lot of grass patterns were repeated.