You would probably have better results by shooting a wider sample (-2, 0, +2). The scene itself doesn't have a lot of dynamic range to begin with, but had you shot it with a wider bracket, you'd have brought out the the contrast between the trees and the shadows on the trees caused by the clouds (which would be kinda cool, I think).
But, noting the position of the clouds vs. the shadows, this was shot in a lot of overhead sun, which is going to be hell HDR or not to eek a quality image that doesn't have a lot of flat lighting going on.
Also, in post, you could try boosting the black point a bit. It runs a small chance of mitigating some of the haze (not by any means guaranteed) and fortifying some of your saturation levels.
The most important thing to remember with HDR processing is you must start with a scene with (drumroll) some amount of appreciable Dynamic Range. The scene here is not ripe with a whole lot of highs and lows, thus the HDR processing isn't going to inject that into the image.