Actually a good shot, but the crop could be closer, as Mag said. Also, you did very well on the desat areas except on the left side you missed a sliver of the original bud.
Not a bad idea at all, and not bad execution. I wonder if a touch more contrast in the mono areas might add impact - there isn't a great deal of differentiation there, and it seems to fall completely into the midtones. More light and shade there might serve to set off the softness and delicacy of the rose very well.
The rose seems to jump out against the desaturated background. IMHO leaving color in the leaves closest to the flower (the two in the foreground) would have added some variety of color and made the shot even better.