Finished my tile, edited my post above. Got a couple crits for some of the tiles so far
Tile#15: I find the dithered highlight doesn't work here. The highlights on 16 & 17 suggests a more reflective and smooth surface, which makes your dithered highlights and the darker shades(to a lesser degree) feel out of place. I think you can have dithered highlights on your tile, but you need to create a transition to show that you're going from wetter, smoother to dryer, grittier ground.
T#16-17, I think there are better ways to suggest texture then the specs of dirt you have(the 1x2 pixels with a light pixel on top and a dark pixel on bottom). In another thread Dhaos pointed out to me that you don't need to have to use every space on a tile. Using these dirt specs in a less unifrom manner and by concentrating it in certain areas could have a more pleasing effect.
T#53-54:Looks good, but the iguana-lizard creature doesn't quite have the optical illusion of bending around the corner. I think it's partly becuase of how you use your highlight, and I think the lines are playing a part in this, too. For the highlights, removing them on the darker side(look at the collumns) would help a lot, and as for the lines, try looking at your rock the lizard sits on and compare them to your lizard. Probably a good thing to do is make a guiding line that shows how your rock bends.
The collab is looking realy good, so far. TakaM, as I said above, you really got this off to a wonderful start. Adarias, your lush vegetation is beautiful. I was a little curious, when I saw you pop in, how you would make do without access to all sorts of crazy colour combos. I am very pleased with the results, you've got some pretty solid skills with that 1x1 brush. I must get going now, so sorry to anyone else I didn't mention.
One thing, I'd like to take #13. I got a nice idea for it while C&Cing #15