Overall, I love the tranquil, abstract feel to this. You say you just "messed around;" I say, "okay, but you still did it skillfully."
The gradient shading and different colors you used for the circles create the tranquil effect. I espeically like how the turquoise, white and dark blue form a light contrast.
As a matter of fact, you've inserted contrast into almost every aspect of the wallpaper; though at first glance the viewer sees only circles, a second, closer look reveals your subtle use of the slightly shaded hearts and rectangles. The only critique I would offer here is the single, solid line that you've placed in the near center of the wallpaper; at the second glance, it seems off balance and a bit out of place, which i find rather distracting.
Overall, though, this is great! All the aspects tie in very nicely together to form a simple, yet modern wallpaper that is interesting and abstract without being overwhelming or overdone. Nice job!