I purchased this program a couple weeks ago specifically because the HDR merge in LR doesn' do the best job, and more importantly, you don' get any say in how it merges the images. Photomatix solved that issue for me and added some nice extras like being able to use their brush tool just like a layer mask to blend specific parts of one layer back into the final image. And it dies it all with a simple user interface.
Yeah.. I don't even know how HDR merge works in Lightroom, cause in my experience it looks like it just takes the middle image and moves the sliders around.
OP, if you use Photomatix, use the exposure stacking options if you want to stay away from the cartoon zone. Everything else is known as "tonemapping."
It is a bit deceptive, but LR's HDR tool basically combines the exposures to give you more data to pull from. So for example, if the DR of your sensor only let you pull shadows up by 1 stop, the added data from multiple exposures might now give you 2 or 3 stops that you can pull the shadows up, highlights down, etc. Think of it as though it's creating a RAW file on steroids with lots more data to pull from. This of course gives you a huge file and then you have to try to edit it like you would any other file. Some people might like that option, but I prefer to be able to tell the program up front how I want the exposure to land and to have the option to preview the final image and tweak it before starting the blending process. It just simplifies things for me and usually eliminates the need for me to pull it into PS to do selective adjustments. Thays just my opinion, your mileage may vary..