Wow, am I glad I got to see this one. We are nearly at rollover, and I don't know how much longer this batch will be up. In a word: I really, really like your image.
Yes, DPCers tend to grade on a curve, and there was some stiff competition in this Best of 2009 Challenge. Your comments already tell you you were over-saturated, under-saturated, and on and on. It's a perfectly adequate image and a fun one to enjoy for its splash of color.
The one nit I might pick, (and that's why I'm here) is the crop. If it was mine, I might remove the left section that has the few stray petals in the upper corner. this tightens up the composition and saves a viewer from trying to fill in the missing pieces.
I love the explosion of color and the shine on the undeveloped sections of the seedpod.
Fun image. (I also took the opportunity to enjoy a bit of your portfolio - there is surely some very nice work in there.)
The fence in the top right of the image I feel detracts from the field of flowers that you have chosen. A little of time organising them would have helped, especially the very front flower with the turned up petals could have been moved slightly to improve the composition
Love the vibrant yellows and oranges that visually pop of the page. This sunflowers are lovely to look upon. My only critique (a small one at that) is that I wish the sunflower in the forefront was in the same sharp focus as all the others. Increasing the F-stop (8 or even higher) and slower shutter speed to let enough light in would greatly increase your DOF (Depth of Field) for both the background and foreground.
They're such happy flowers! I think this shot might just be lacking a bit of punch, it's not the colours which are really strong and vibrant, I think instead it's the light, which feels very flat, like you've taken it on an overcast day.