The first two images are tastefully done if you're going for the stylized HDR look without being too over the top. I wouldn't quite call them natural-looking though. I'm not a big fan of this look, but I seem to be in the minority and I'm sure a lot of people will like these. You've done a good job of avoiding halos and inverted contrast. In the first image the sky is a littleover-saturated and slightly greenish. In the second image the sky is a bit under-saturated, almost gray in places.
Processing on the second image is very natural looking. If you're looking for HDR to tame high-contrast scenes and make them appear as the eye would see them, I think you're on the right track with this one.
The last one makes me want to squint. I think it's a matter of too much "detail enhancement" and not enough realistic tones.There should be shadows on the left, and the fact that they're not there makes it visually confusing. The image is very 'crunchy' and digital looking. They sky is also a little splotchy.
Tips for natural-looking HDR in Photomatix using detail enhancer mode:
- Go easy on the strength, luminosity, and micro-contrast sliders.
- Use the smoothing sliders. The global smoothing slider goes a long way toward making images more natural looking and will prevent things like inverted contrast. The highlight smoothing slider is good for preventing those uneven skies that are over-darkened in areas.
- Set the Black point to something other than 0%. There should be some black in an image, otherwise it looks flat and unnatural, especially when it's a high-contrast scene.
- Use the gamma slider to set the midtone brightness, not the luminosity and strenght sliders.
For the 'natural' look, you may want to investigate Tufuse and Tufuse Pro, which I find often produces more natural-looking results.