Monster Hunter 4 is the 4th numbered iteration in the Monster Hunter series and the 2nd on the 3DS. It expands on the 3D movement of the series adding climbing and such.
In general, the game plays pretty similar to Monster Hunter 3G. You pick your gear and choose your class to hunt monsters to build better gear to handle the stronger monsters and tougher quests. Monster Hunter 4 is different from its predecessors in its strong emphasis on three-dimensional movement. Walls can now be climbed more fluidly and in any direction, and for the first time players can grab on to monsters and attack them, as well as attack while in midair. Some monsters are also terrain-aware and will use it to their advantage There are 2 new weapon classes: the Switch Axe and the Insect Rod. The underwater fighting of the previous game has been removed. Online is fully accessible in this version unlike Monster Hunter 3G which required the Wii U version.
Famitsu gave the game a 38(10, 10, 9, 9) out of 40. It was one of the best selling games of 2013 in Japan, only falling behind Pokemon X and Y. Monster Hunter 4 sold more than 1.8 million copies in its first two days on the market. As of March 31, 2014, the game sold 4.1 million copies according to Capcom. There is an upgraded version due Fall, 2014 in Japan called Monster Hunter 4G.