Happy Dance Collection intended to make J-pop fans happy
As if the fact that it's only being released in Japan (as of yet) and the J-idol theme aren't enough clues, Happy Dance Collection is a very Japan-focused game. Namco Bandai is aiming squarely at the female Japanese audience with this game, which does contrast a bit to the variety of J-pop, European dance and other stuff usually found in the Dance Dance Revolution series. There's no E-rotic to be found here, for example.
Siliconera has posted a translated list of all the known J-pop songs appearing in Happy Dance Collection, which includes recent releases like Orange Range's "Ikenai Taiyou," and Greeeen's "Ai Uta" as well as more "classic" songs like Morning Musume's "Love Machine" and Koda Kumi's Cutie Honey theme (well, 2004 is kind of in the past, right?)
