They are very pretty indeed. If they have to be criticised then here is what i can think of right now. The composition may have been more interesting with the center slightly more off but i am not sure, it may just be best like this but i am sure someone will say different. Sometimes reds like this can be a bit overpowering, but i think the anther and stamens calm it sufficiently, they could be a little less soft in places, I have heard people say they dont like that either but hey, it doesnt stop them from looking great as far as i can see. I also like what you have done to the sunflower, the white edges between it and the thresholded background and the bee really make it for me.
tim