Technically, this shot is an awesome shot. The exposure is right on -- details are present throughout the flower and there aren't blown highlights, etc. The lighting is good and even without being harsh. The shallow depth of field works well to isolate your subject and make it look even cleaner and keeps the background from competing with the main subject.
Compositionally, it feels balanced and "natural." The flower is sitting roughly on the third, so while I am not a stickler that it be exact (but I didn't vote), since this challenge was the rule of thirds, I suspect many voters may have wanted it exact. Even so, I think it would have also been a nice shot. To put the "things" that are sticking up (I am so botanically challenged, sorry) on the right vertical third and the petals on the lower horizontal third would have caused some of the flower to be out of frame, but I think that might have been okay.
Overall, this shot is a very good one for the likes of a botany or flower magazine, or one of those books similar to a trail guide that helps you to identify various plants and things. Emotionally, unless a viewer just has a passion for flowers, it may not elicit a great response, and that could explain the 5.5 rather than a 6 or higher.
Again, this is an awesome shot, and one you can be proud of!
7 - Nice shot. Well done for the correct name in the title. Criticism; while no expert in this 'rule', for this Challenge, I would like to have seen an even stricter application here. The 'red' in the background detracts in my opinion, so a tighter crop (or different angle), nudging the flower and "point of interest" further into the 'intersection', would have made this a better shot in my opinion. Nice colors, good focus on the flower detail, including the leaves.