I picked up the game last night, and have been playing it like crazy. I also picked up SuperNOVA 2 at the same time, and I think I'm enjoying Hottest Party more simply because of the hand motions.
The hand motions are a really simple gimmick, but it just feels more complete dancing with the hands. Its harder, requires more coordination, and is just a lot more fun to play (and watch). That being said, its nice that I can also turn off the hand motions (and the other gimmicks).
The lack of modifiers (like increasing speed) is disappointing, especially since there are lots of slower songs. But there are also lots of harder songs, so its certainly not watered-down like Mario Mix.
I hate the character design, but I like the fact that the characters actually know what they are dancing too and aren't just doing random canned moves. Its more fun to watch, even though you should probably be paying more attention to the arrows than the dancers. The interface itself is really happy and peppy, colorful and clean, and I like it much better than SN's interface. The announcer for this game can get just as annoying as the other games, but I think I like this guy's voice better.
The track selection isn't that great, but it isn't that bad either. There are a few great songs, and some really fun ones, but overall its just decent. Some DDR favorites (Love Shine and Candy) have been remixed/redone in English, and its really interesting to hear. Still the same songs essentially... just in English (forgive me, I'm not aware if English versions of these songs existed before this game - they are new to me).
Overall, I'm liking this better then SuperNOVA 2, though not by much. The hand motions make things fun, but I hate all the other gimmicks (and turn them off immediately). I hope Konami makes another game for Wii and works on the other aspects of the game, as the gameplay itself is a great as ever (at least, in regards to DDR).
Now back to playing...