Big Ben and houses of parliament Depth of Field being used creatively - I feel this gives a much better effect than having shot the image with a smaller aperture which would give a bigger focus in the image (so Big Ben in the background would have been in focus too).
The texture in this image is really interesting as the icicles against the metal are really intriguing. The background being blurred creates a more up close and personal feel to the photo as it looks like you're invading its space by getting so close to the chain.
Autumn tree: I like the angle of this shot because it enhances the trees large size. Additionally I like the shallow depth of field, focussing the lower leaf yet enhancing its colour with the out of focus background.