Detail: good!
Background: I'm glad it's out of focus. Great noise control. I wish it was either all green or all gray
Pose: I think it works. I wish we coudl see the tail
Composition: I wish for more space in the image, but I suppose since the perch is so ugly you probably don't want a whole lot more of it.
Colors: Good - nice and warm. Good even light.
This guy looks quite big and rounded compared to most Chipping Sparrows out there :-) The perch is less than ideal, but I like the pose and BG. I find that these guys are one of the easier species to lure onto perches via audio (if you are OK with this type of technique).
Mathew and Daniel both made all the comments I would have.
I used to dislike "it would have been nice if......" comments but have since learned it REALLY helps my composition when shooting.