Hi, some wonderful stuff here, you definitely have come a long way. Love the design of the wall and guard towers.

On cracks - horizontal cracks occur in rocks where the layering of the rock is horizontal, yours mostly diagonal, and in the most recent image - going in all possible directions. If the layering(or whatever the actual geological term is) was horizontal, the crack might work out too. http://www.watersheds.org/earth/layers.htm

On the wood texture - You have done a great job on the details! A couple of things though...
If you plan to tile it, then some of the detail might be too specific and that will stand out a lot if the texture is repeated several times over.
The underlaying shading looks a bit indecisive. For natural form it looks much too straight and for man-made curvature its too blurred out.
For a more natural look you might want to increase the saturation for mid-tones and shadows and turn it down for highlights. The bump map effect does exactly the opposite.

There is a huge problem with converting from a non-polygonal to a low-poly format. Automatic optimization is ussualy very bad, especially if you have any curved elements. You will most likely need to export them seperatly.l Its also very likely the you will have to merge a lot of vertices, might not be that hard to do, but the normals of the faces will most definetly be changed in the process and mess up the uv mapping. I used a method in which i drew seperate polygons on the existing nurbs-model, but it takes a lot longer than building the actual model. Since you will have to unwarp the model in something that is not sketchup anyway, it might be easyer to start with blender.
Sketchup is a good tool for "sketching" ideas, but you will need a lot of tweaking before you get a good low-poly model. A good modeling tool for someone who wants to use nurbs like edditing methods, but needs a low poly model as an end-product is Cinema 4D, but unfortunaltly is a commercial product.
Also.. Bricks are evil!
It might be a good idea to avoid using any large areas of brick surfaces, unless you have really good textures, and so far i have seen extremly few, pure photo-textures won't do. The contrast between the bricks and the seams is ussualy too great, partly because it lacks relief and on flat CG surfaces gives a very different look that in real life. Some repetetive color patterns will also be instantly recognizable on a large scale, making it rather annoying to look at.
...which leads me to large surfaces in general... its ussualy not a very good idea. Try braking up the space with some constructive elements, this will help to establish a human scale and patterns in textures wont seem so annoyingly repetitive.

Saying that all oddness is intended is avoiding critique in general. 
It might be a good idea to start with modeling a mesh, to define the overall shape in something other than z-brush.
Z-Brush isnt very good for defining large gestures like the jawline, setting back the eye sockets or compressing that ball you started out with to the shape of a skull. It lacks precision and the result looks blobby. Once you have the defined the basic shape it is almost impossible to go back and change it, so you should work more on it before adding any details like eyebrows. You should also looks  for some reference images that devide the head into simple planes, to see the breaks in form. Patting your face on the front and on the sides also helps. The break  in form is much sharper than most people realize. This form is one more reason to not use z-brush for the overall shape - its just very hard to redproduce it with brushes.

Woot, a doomsday thread with a hint of philosophy! I wonder how its not locked already.

I don't feel dead yet, so i guess they failed at destroying the world.

Eliseth: you are scary  ...or just attracted to big buttons.
And i don't see why i should be dead in the next 5 years. Is there yet another doomsday, or the 100th take of the day of Judgment? Or maybe you are engineering a big red button that can destroy the world? Spreading such rumors can be profitable if you own a sect or two... sadly im not charismatic enough to get one going.

EDIT: I didn't believe this experiment could cause the end of the world until i saw this: http://www.youtube.com/watch?v=j50ZssEojtM&eurl
EDIT2: Its the first funny thing i have seen on youtube.
Im about to drop some particle physics in da club, yo!

Yay, another n00b bashing thread about a lost time when grass was greener and people read books.
I dont see how reading LoTR gives someone imagination. Thats pure nonsense. Most fantasy books are written for enjoyment. A lot of them are very generic like the flood of Asian MMORPGs. Because people read such books, they usually RP godmodding orphans. Death to all parents!
Powerleveling and RPing can go together. Its just like people who spend countless hours in the gym or artists who draw every day. In real life these people get praised for it. Can you imagine anyone calling a musician a f-N0.0b just because he practices very often?
As long as the player stays IC and dosn't go LoLzoring around, i don't see a problem. You cant force people to enjoy the game exactly the way you want them to. Thats a very selfish thing.

Do the schools of Argan, Esteria and Lah’ar have connections to any religion in particular?  Where are they practiced? How do they get taught? Are there any important figures?
How dose this relate to the Ahrijani? What exactly is practiced/taught in the monastery of Ahrija Agat(what school?) What is the history of these schools and the monastery?

Haven't been ingame for some time(and now i cant get in), but last time i checked there was no information on these subjects.

Your tree rendering technique is simply incredible. The last one reminds me of human forms captured inside the tree.

Not that i dont belive this, but there is no need for Photoshop to fake it. Just take a screenie and display it as a photo on the iphone. As easy as that. People just think too much of Photoshop.