I'm always trying to catch Magpies in flight. They're very quick! You did well to freeze the wings, but the main problems are:
1. He's flying away from you - rarely are photos of the back end of a bird interesting.
2. The dark grey sky - doesn't do his plumage any favours. Magpies have wonderfully iridescent plumage that shines purple, blue and green when the sun catches it.
3. Lack of detail - The black feathers are solid black. There's almost no detail at all in his feathers and that is one of the main reasons for shooting birds, the patterns and colours of the feathers are what makes birds so beautiful.
I would put this one down to good practice. You know how to freeze the wings and frame the subject correctly, but you need to get in front of birds to get a decent shot.
Also, learn their behaviour. You'll find that birds are much easier to photograph during landing because they slow right down and some hover briefly before touching down which makes for much more dramatic photos. When birds land, they spread their tail feathers to act as airbrakes and spread their flight feathers to act as flaps so they can slow right down but still stay in the air. These make the best bird shots as you can then see the detail and colours of all the feathers. If you can catch them on the down-beat of the wings too, you'll have the perfect shot. The down-beat shows the power of the wings.
But remember to get either below them or at their level. Shots from the top of birds at normal eye level are boring too.
The best birds by far to practice this on is ducks. You can see them coming to land from a mile off. You'll see them gliding with their wings held in a square-ish position as they lose height and just before they land they stretch their feet out in front of them and beat their wings to slow down, then they ski along the surface of the water to slow down further before stopping.
This process last about 3 seconds, but as their glide down is a bit longer, you have time to zoom and focus. When you get those shots perfected, try the same technique with other relatively slow moving birds such as herons, geese, swans (which are amazing), crows or if you have any in your area of the US, eagles!
Here's my favourite shot of my duck practice!
Gear down by
Forkie, on Flickr
If you look at my other bird-in-flight shots in that set, most of them are ducks, geese, crows and seagulls, all either landing, or slowing down to pick up food off the ground or water.