Like the perspective and the pose. May be a bit more sharpness as already suggested. One thing I'm not sure is whether it would improve if there's more room on the right of the bird. But your crop as presented is totally understandable. Nice job catching the kestrel.
You did extremely well to capture this bird in flight. They are so fast that it's tough to do. The vivid colors, fanned tail and head turn really send it over the top for me.
The fanned tail is what separates this from most Kestrel images. They are always flying so fast I never realized the dominance of Grey on their wings. One of the better KIF's I have seen.