I am quite impressed with the geometry and the expansive feeling of the age, evident even with just 2 screenshots. Very excited to explore this in the future.
Your island edges remind me of the ferry terminal in the cavern in a good way. I'm already curious about those structures in the distance.
Personally, I wouldn't worry about the high-poly geometry unless you actually have performance issues yourself. Someone seems to have made everyone paranoid about high detail geometry, while the only real occurance of it was the case of the subdivided bookshelves.
But, you asked for criticism, so here goes.
Lighting, I notice, is mostly vertex based and seems to show the telltale signs of being done by plasma, rather than blender. While this is good for getting matching avatar lighting, it isn't quite adequate for the body of the age. For the moment, though, it would be a good idea, if you haven't already, to kill the 0.5 ambient lighting that is the default in blender materials, so that everything isn't so bright gray where it ought to be unlit. In the final version, I would definitely go for some nice baked light to show a long shadow from the building, etc, but it probably isn't time for that, since the age geometry probably isn't finished. Although some people have commented on the color scheme in your textures, I think that the lighting is actually the root of the problem, I think that with some good orange mood lighting, and reduced ambient to match the sunset-like sky you have in place, the colors would even themselves out, as they aren't too far off of what one would expect to see on any given brightly lit surface in the real world.
I'm guessing here, are the gold bands around the middle of the orbs on the railings supposed to be the light emitting parts? (are they supposed to be light-emitting at all?) If so, I would suggest putting a few flattened flares around them to show the glow effect
The water looks bright green and goopy, as if it had been polluted. Of course, I wouldn't actually hold any water issues against you, since we haven't gotten nice reflective plasma water yet.