I shot this one today. It was pretty hot out there but nevertheless I was really wanting to try the new EF 100mm f/2.8 USM Macro lens. First result, and I personally am impressed by the quality of this lens.
Since you asked for a critique, I have to first ask, "what did you envision as the subject?". It's a bit of a rhetorical question since it is obvisously the bee. Nevertheless, the flower does jump out at the viewer, taking the attention off the bee somewhat. How about a tighter crop (or capturing a closer image), which isoloates the bee while putting it in a "rule of thirds" layout? Maybe something like this (but larger).
Definitely stop down. As a result of this, you'll either have to increase ISO or provide light. If you have a flash, you can trigger with the canon equivalent of the SC-28 or other and make yourself a cheap diffuser out of paper towels or something like url=//www.flickr.com/photos/lordv/201782132/]this guy.[/url]
Check out his stream for examples of what you can do with such a simple setup. Using a cord will give you flexibility to position your flash from different angles and make the light better since it's off camera. Just hand hold, unless you want to invest in a bracket.
As was said, try not to cut off the bit of the wing. Pretty good outcome from your fist venture though.
I like the dead-on front view of the bee, colors are strong, but natural. maybe a little too centered for my own preference and the bees wing ios a bit cut off at the top. I like the bit of iridescence on the wings. In a challenge I would probably give it a 6. I like bugs, but I'm not a huge flower fan, so a closer shot of the bee would probably get my interest more.
Looks pretty good to me, perhaps using A mode and f8 might have grabbed a deeper DOF. With Macro lenses it takes a while to get used to them, I found using continuous focus rather than single focus works well as the little buggers do tend to move about. Stick with it, you will get a great deal of satisfaction from the Macro lens.