Tough bird to shoot in flight. I think given your shutter speed that this should have been sharper. What f stop did you use? Also needs to be composed so that the subject is not in the center of the frame. Move it left and leave some room right for bird to "fly into".
Chris, I think we can all appreciate the difficulty in obtaining sharp images of small birds in flight but I have to agree with Joe that as posted the swallow is soft (especially the face area). This could in part be due to a heavy crop? Perhaps another round of USM would help. Still, not easy to track in the viewfinder so you did well there, and with a nice wings down position.
In a situation like this I would also not be afraid to bump the ISO higher to put more chances on your side (e.g. here ISO 400 = 1/4000s. !). Also agree with the composition...by placing your subject on the left side of the frame it would give it more room to "fly" into...just an aesthetics thing.
Yep, Christopher, I know very well how difficult it is to capture these guys, so you have done well to get him in the frame. Maybe a large crop, but well done on capturing a very fast character.
You have done well to capture one of these erratic speedsters. Dan has covered the important points well. Image quality from a a presumed heavy crop is what is letting the image down. A bit more sharpening will help a bit. Selecting the BG with colour range and then applying a curves adjustment to lighten the blues and darken the reds will give a bluer BG that may show the bird off better than the current grey. Keep at it. A fuller frame image will capture more detail and a higher iso will keep motion blur to a minimum - there is a lot of luck needed in addition to the skill of tracking one of these.