I don't know that I can add anything to what lucidlotus said, but I'll try.
Compositionally, I think it might have been stronger if the bubble had been more in the corner. I think this kind of shot lends itself well to negative space and makes the surrounding "texture" even more ominous to the future life of the bubble. The color of the background is a bit distracting, though I like the texture.
Technically, while the uneven light can add drama to the shot, in this one it serves more to pull the eye from the bubble to the light spot. (If my understanding is correct, we will subconsciously "drift" towards light and "ignore" other details. That said, the shadow of the bubble is very intersting, but perhaps too subtle. Bubble are boogers to photograph, and I think had you used a lower ISO and slower shutter speed, that may have "darkened" the background and given some nice color trails as the bubble floated and met its eventual, though unavoidable, demise.
Hm.. this certainly meets the challenge but I'm afraid that is all it has going for it at the moment. Clearly the bubble is meant to be the focus of the image and I think this could be a great idea if a few things were changed:
Background: Rumpled and grey and doesn't do much for the image. I would recommend a black for this type of photograph.
Focus: is GREAT.. unfortunately.. its on the wrong thing - the background. The focus should be centered on the bubble and thus let the background fuzz away, this I can see is difficult due to the nature of bubbles, cameras tend to have a problem finding them to center on.
Lighting: The lighting is actually pretty good, if there was a way to center it more spotlight-esque only on the bubble, that *might* give the camera more help in focusing there too. I can't be sure though. Still your use of light was good.
Composition: Here's a biggie. Right now you simply have a bubble with nothing too exciting going on. This CAN work, but the other elements of the image (background, focus, etc) are working against you and so the simplistic approach didn't really fly. I do like the idea behind the image immensely, I can envision a simple, classicly beautiful perfectly rounded glowing bubble suspended against a black background of some sort.. simple and lovely. So the idea and intent is there, it just didn't manifest itself this time around and led to a fairly dull image.
You have a good eye and vision, just need to work on the technique a bit to bring those up to match. I gave a 3.
The funny thing here is that I find the backdrop more interesting than the subject! - Having the bubble out of focus and fairly centered in the composition also tends to draw the eye to the backdrop. Nice title. And the shadow is pretty good (the faint pink in the shadow works well)
It looks like the camera focused on the background instead of the bubble. The bubble seems to cast an interesting, rainbow shadow, but the background is so dark and wrinkled that it serves to distract.