Grahame, I see a couple of things you could improve on here. First, let the bottom of the stem come from the bottom of the frame and then swoop across - that tends to look more "natural." Also, I think this is a tad bit light on DOF - the top of the rose is really not very sharp. I'd take the exposure up a bit more, too. Remember, you want to expose for the light tones and then darken the deep tones in pp if necessary. That way the light tones don't have much noise but you get the dark BG you desire in the end. Another way is to use flash so the front of the image is well lit and the back falls away into darkness.
The angle of the rose and the bud are lovely. I like the green things at the base of the flower going in different directions. Lightening it up a bit would improve the image.