I honestly can't explain the lack of sharpness. Maybe f/32 introduced difraction; that would explain some strange coloration. My recommendation would be f/8 and at least 1/1000, with manual focus for critical sharpness. 100mm f/2.8 macro and 20d are an excellent combination, and with adequate technique and lots of practice, you'll work miracles with this thing, shooting insects.
Thanks for the critique, Denijel - I always like constructive critisism. I think some of the detail was lost by having put the aperture to the limit (F32 - to get the most DOF for this difficult shot), and by the fly being busy flying when I took it (possibly not perfect focus). The cropping was quite a lot, but I don't know if I would term it extreem. I have attached the uncropped version for you to look at, if you want to add any other suggestion...
It looked excellent on the thumbnail, but in magnification it lacks sharpness and detail, and the background is confusing, tends to lose the subject. I'm left guessing if it's an extreme crop of some kind, because this combination of lens and camera can give ten orders of magnitude more. But the idea is great, and I recommend that you try again until you get it right.
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