I get great results with Photomatix fusion, but you really need to use the right set of exposures to get the most out of it. You need to take the time to get a understanding of how it works, and you need to experiment to do this, and for any kind of experiment, your going need many more brackets to try out than just 3, try as many as 9. Once you get to know how its works, you'll have a better idea what you'll need.
Take the shadows as a example, when I first started using Photomatix fusion, when looking at my bracketed images, what I thought was way over exposed and useless, was in fact just what I wanted to include in my bracket set, even though it was almost white, that is where the deepest shadow info was, with out this very over exposed image, it didn't work, and I couldn't make the very small changes that make it look realistic, the same goes for the highlights.