Would have been a great shot if your shutter speed had been fast enough. I would have said 'good composition' but it's obviously been cropped. I suspect it's a crop too far and you didn't have a long enough lens to get the rider and bike large enough in frame. Your instincts are good though - if you can get your shutter speed up and create that kind of composition in camera without severe cropping then you will have a top image on your hands.

Exposure is spot on, well done. What a stunning structure! Personally, I'd have either liked to have seen either precision symmetry or definitely angled, not something just off-centre (probably the former, given the subject). Also, the image isn't as sharp as it could be, probably due to the slow shutter speed causing a bit of camera shake and the wide aperture not giving enough DOF. As it's so nearly a really good shot, I'd be tempted to go back under similar lighting conditions and take a tripod so you can shoot with a smaller aperture/greater DOF and it won't matter how slow the shutter speed is. Of course, this is wishful thinking if the cathedral doesn't allow tripods up there! Actually, thinking about it, although you shot this with your D300, you have a D3, don't you? Lighter answer than tripod - whack up the ISO! Seemples!

Suggestion for next time - if you are trying to flatter a lady and make her face look slimmer, then have the light hitting the side of the face away from the camera. It's called 'short' (American) or 'narrow' (UK) lighting. The light you have here is 'broad' lighting and it does what the name suggests i.e. broadens the face. (Great for anorexic supermodels!). A touch of reflected light to the left would also have lifted some of the detail out of shadows. You have captured a lovely, content expression in the bride - well done for that.