While Nintendo's 3DS Conference was the site of several major announcements for RPGs like the new Fire Emblem and Bravely Default, the biggest announcement of the conference was that Monster Hunter 4 was coming to the 3DS. Previous main entries were on home consoles and the series has been a powerful force for the success of the PSP in Japan, so this is a major triumph for Nintendo's young handheld.
The only information revealed so far about Monster Hunter 4 is the trailer below, which was shown at the 3DS Conference. It is unknown how much this "concept" trailer is indicative of how the game will actually play when it is released, but it does show off many gameplay elements that are new to the series.