Picture, as promised...
Here's the forum's latest threads and comments on the regular version of Tapatalk.
Here's the same information as viewed through Tapatalk HD.
Basically, I would compare the HD version to an email program. You have the latest threads on the left side of the screen and the posts within that thread on the right.
The one down side I see to the HD version is that it isn't a universal app (at least in the iOS App Store) like the non-HD version is. Tapatalk HD is for the iPad and Tapatalk 2 (which appears to be like Tapatalk HD) is for the iPhone/iPod.
This is my take on Tapatalk HD. I have no experience with Tapatalk 2.