First, it looks like you are off to a great start! I'm working on a large scene as well and it is going too slow!
You've already chosen a general style for what you've been building at it looks good. I really like what is going on in this image:
I would certainly focus on the landscaping and paths (there are some pictures where this is done well, others that look like you have work to do). The amount of elevation changes you are incorporating into the MOC will really make it pop, especially once much of it is covered in foliage.
The round walls look great, but do appear more 'complicated' or run down than the flat walls. I don't think there is anything wrong with this, but you could put more 1x1 round bricks (and plates) into the straight walls to even out the texture.
The dark bley corner of your tower (in the image above) looks a bit flat. Having 1x2 tiles sticking out would look a bit better, IMO. You use the same technique with the white an tan, and for some reason, I like it better on the white and tan as you have it.
Will all the water look like (or similar to) what you have shown in the image above? I hope so, it looks nice and you made a good transition from land to water.
I like your roof style.
I'm not a big fan of the 1x tile cross bars in your tutor building (below). Many people have done this, so this is likely just me being picky. Finding an alternative technique is almost impossible without redoing a bunch (or using wall techniques that appear much more 'crumbly'. In this situation, I'd just remove the diagonal beams. The house itself looks great. I'd use brick/plate built doors, but the black ones fit well.
I like everything in the image with stained glass (below). The ivy climbing the walls and the landscaping on the ground is great. I would cover some of those exposed 'open' studs with tiles or vegetation to match your other walls.
I cannot wait to see this all done and together! I'm not sure how much rebuilding you want to do (if none, I completely understand, disregard those suggestions).
Others have responding to how to post pictures, what I do is right click on the image, select "copy image address" and paste. The Eurobricks editor will automatically insert the image for you (assuming the source is on a secure website: https). For flickr, I go to 'download', choose 'all sizes' click on the size I want, then right click that image.
p.s. cool space ships in the background of some of your images.