I didn't really like HDN very much actually, it felt like there were too many hoops to jump through. The Terraportation thing was just annoying, I wasn't a big fan of the grid-like dungeons, and the combat really felt flat. Items and healing were a pain, battles dragged on and I just skipped animations. I had a whole bunch of gripes really. The only reason I played it as long as I did was because I liked the concept of the game.
HDN2 improved on basically all of my gripes. They tried a lot of new things, not all were perfect, but I love the new combat, the large selection of playable characters and the myriad little systems. Combat is the biggest thing for me though, it felt like a chore in the first one, in mk2 it was actually fun. My only issues with mk2 come from the lackluster pacing and writing for the story. A little more time spent there and I feel it could have been something really special.