The ability to play upto 4 players simultaneously and better integration with the Wii should make this one better. I only played a few of the minigames and it would have been nice if some of those were multiplayer.
Yes, it is similar mini-games like Wario (never played, but read about).
In the first Rabbids you do each game to uncover a piece of a puzzle. The games apparently last longer than Wario.
From what I can tell, you don't need to by Rabbids 1 in order to enjoy Rabbids 2, since they are heading down a slightly different path on 2.