Just a few points...
On the plus side, it looks like you've got out of the habit of intersecting geometry....do you notice the difference?
On the downside there are a few issues...well one main one really and although I noticed this in your last project I refrained from pointing it out in the hope it was on your 'to do ' list....I guess it wasn't. :biglaff:
Anyway...whatever the Blender equivalent of 'Smoothing Groups' is you need to add it to your 'to do' list....its the one thing letting you down now, and as your projects get more complex and refined its beginning to stand out.
Take a look here and notice the 'faceting' on the surfaces....this is due to the lack of or incorrect 'smoothing groups'. (Or whatever the Blender equivalent is)...
Also note those parts circled in blue, see how smooth they are? Did you edit those parts? My guess is you didn't. In the software I use, smoothing groups' are applied automatically and are only changed when the object is edited at sub-object level....poly, edge or vertex.
Its important to keep an eye on them as it can really make a difference to the render.
The right smoothing will also sharpen up areas as indicated below. There is nothing wrong with the geometry but polygons at right angles and with the same smoothing group will instruct the renderer to 'smooth' out the two.....which in the case of the gear teeth you don't want. place the polygons in different groups and the render will render them correctly.
Again, notice how the blue circled area looks much better...
large flat areas can also be affected by not having a smoothing group assigned to them, although in the following case it may be more a lack of geometry than smoothing....difficult to tell without seeing the mesh...
On a different note....spot the difference here...
Why is there a 'gap' in the left hand pipe? A minor point and not really wrong but unless we can see a reason for it being like that it does look like an error....especially having the others as a comparison.
Of course none of this is crucial for the actual image you intend to use, it wont be seen, but its the small things that add up to an overall much better image...its just good 3D practice to be honest.
Overall pretty good, but learn about those smoothing groups!!!...(or whatever Blender calls them.)
Regards.
MrToM.