|Hi Chuck, welcome to the critique zone!
My inital take on this image is that while this was taken at night, it doesn't really show apart from being a little dark. You don't have a real 'night' feel to the shot, so what to do?
Technically: This is a pretty noisy image - not only have you got ISO 640 in play, but also 'long exposure' noise. Your use of f8 has also given you a pretty big depth of field which I'm not sure you need. I would drop the ISO and the aperture (maybe f6.3 and 200?) and take the hit on the shutter time - it should be cleaner. You can then run it through noise reduction in PP. I also suspect that there is a long exposure noise reduction setting in your D90, don't know if it was on? The natural lighting is interesting on the foreground, less so in the background although nice in the sky on the right.
Artistically: This is of course completely subjective, but... I would have taken this shot from slightly to the left, focusing on the big pumpkin left of centre, moved a lot closer and put that probably slightly right of centre and a little low. That would give the photo a real sense of focusing on the pumpkins. It would also block out a little of the background. If you want the field look in for Charlie Brown, you could start a little above and have two thirds ground in the shot. If possible, I would have definitely done a 'recon' during the day, composed the shot, and then come back to take it at night.
PP: You don't say what you did do, but I suspect that a little Noise Reduction, sharpening and popping the contrast with curves or even levels would have boosted the look of this a little.
Random thought, this could be a great location for 'painting with light'? ie. Sticking the camera on 'Bulb' and then using a big flashlight to 'paint' in the bits you want? Worth a play if you have the time. Hope some of this was useful!