I saw the videos. The best one is that ballon fight mode (the puzzle mode, that is not against time).
The first video (that dual-screen multiplayer) was confusing. I don't think I would like it or I would be used to play it when the gameplay area keeps going up an down. I might even get seasick.
On second video... Wtf was that pixelated 8-bit mario with some cheap "3-D" rotating effect? That looks ugly, and looks like they did not have anything better to put there, and it is there just to fill space.
On both first and second videos, I did not understand the relationship between mario/donkey kong and Tetris itself. What was that happening on right (1st video) and on top (2nd video)? Do we control both tetris and mario at same time? If yes, well, that's interesting, but not really funny. And, again, looks pretty cheap, since they used the plain old NES mario on this supposedly new game. Do they think they can still sell the first Super Mario game? This would be the same as Sega putting Alex Kid or Sonic 1 at half of screen, while Dr. Robotinik's Mean Bean Machine is being played at other half.
I don't have Nintendo DS, nor any modern console or portable video games. But, looking at this, I prefer to keep my good and old Tetris mini-game.