Just had a look at all four of these at the largest size on Flickr and here's my thoughts.
No.1 :
I like the pose and you have done well to get a natural expression out of the model.
The composition is great and the location interesting.
The highlights of the dress are blown out, either purposefully or accidentally but either way the image would look better with detail there. Also because that area is now so bright it pulls attention away from her face, which is not what you want.
Focus has been missed and you have tried to save the image with sharpening, this doesn't work and only degrades the image.
The Post processing you have done has removed any skin texture that was there and has also made the areas of different skin tone blocky.
I don't think the cyanotype tone is necessary, in fact I think it harms the feel of the image. The image is of a beautiful woman looking playful and smiling, not something that looks better with a 'cold' tone over it. If anything I'd say a warm tone but personally I'd prefer it straight B&W.
No.2:
Great moment that you have captured here.
Again very well done for how you have pulled the look out of the model.
I'm afraid the post processing has ruined it for me. Her skin on her cheek and hand looks like she is in the final stages of some sort of degenerative illness or she's turning into a zombie.
It looks like you have a really nice image underneath it all and I'd love to see it without all the effects.
No.3:
Good composition and execution.
Nice to see the highlights haven't been blown out in this image, though the dress is brighter at her waist on the left of the image so I would have burnt that down a touch to bring it in line with the rest of the dress.
I think this would have been a stronger image had you persevered to get a better expression from her, as it is the image is nice but with a great expression it would have lifted the image much more.
Again the post processing ruins the image for me, it makes her look like she's just been dragged through a hedge backwards.
No.4:
The composition, exposure, styling and location are good. Except you cut off her elbow. I would have asked her to bring her elbow in as it doesn't need to be out that far anyway.
The rest of the pose is good except for the hands. The skin colour on the hands is badly blotchy because of the fingers being clasped together (never a good idea). I would have had her left hand basically where it is and just rested against her waist and her right hand rested on her hip/thigh just below it.
It looks like you have used either a bare flash head or grid on the models face/neck, the light is far too harsh and has deepened and highlighted the wrinkles. The light needs to be as soft as possible when shooting people with wrinkles that need to be reduced.
It doesn't look like much/any skin work has been done to the face, this does the subject no favours. Learning to do good work on skin can help no end in any portrait but especially when it comes to mature ladies where wrinkles, etc. are noticeable and only get further highlighted in photographs.
Overall I'd say you seem to be a decent photographer but you're using effects that are not necessary and that mostly actually make your images look worse than they are.
You seem to be able to pull good expressions/poses out of models, which is a massive thing! Most photographers that are technically great struggle when it comes to that.
I'd say the best way you could improve would be to stop using the 'effects' and concentrate on producing good, clean portraiture. Your effects are currently hiding the image, if you're image was a meal you've totally covered it in brown sauce.
I'm not saying never to use effects, just that you need to nail down your images as far as good focus, exposure, colour and contrast goes and learn how to make skin look good. Then start to explore the possibility of adding your own style to the images. The effects you use should then only be a slight garnish to your already great portraits.
Hope this helps.
