I don't know about the lens flare... It looks cool, but it's missplaced. The real sun is behind the nose of the jet, just follow the lightrays.
And the horizon, well... it looks acceptable to me, but I think it should be blurred a bit. The contrast is too strong.
And now I'm really looking, I think the aircraft is a bit too light and off colour. Try darkening it a bit or use the burn tool (I you have it) and put a (slight!) colour layer over the whole picture. That might blend it a bit more...
Just talking about minor details here, it already looks awesome.
