It's the next Monster Hunter. So far it's only been announced for Japan. They announced a TON of new stuff for it, so a lot of people who played the previous games are pretty pumped. I'm conservatively skeptical.
The MH4U demo is kinda alright if you want to try out the game. It's not the best first taste, but then again the demos seem to be aimed at series vets. Each weapon plays drastically differently, so if you pick the "wrong" weapon initially a lot of people get put off. I suggest trying them all for that reason unless one really clicks for you.
I can wait till it comes out in Japan cause I have GW with rxTools so I'm able to play it.