- New built-in quest maker feature that allows Hunters to explore a new area called the Unknown Forest, then make their adventures into Guild Quests.
- Can also be shared with friends through StreetPass.
- Unknown Forest won't always be the same whenever you visit its various areas.
- Sometimes paths will be blocked and other times, they may be open.
- The same rules apply to monsters. Won't always be in same spot.
- While the maps won't always be randomized in terms of accessibility, things may still be different on your next trip, meaning you won't be able to continually farm the same areas.
- Maps are also different when compared to regular quests.
- These maps will just show your immediate area of the Unknown Forest.
- Monster Yian Garuga from Monster Hunter Freedom will return in Monster Hunter 4.
- One of the more important monsters in the Unknown Forest.
- Velocidrome and his Velociprey minions also make a return.
- There will also be other monsters such as Yian Kut-Ku and Basarios living in the Unknown Forest; however, they have yet to reveal which ones will be exclusive to it.
- Excavation Equipment, a new set of equipment with unique parameters and designs, which can only be collected from the Unknown Forest.
- Similar to other special items and equipment, they won't be revealed until you complete the quest.
- There is also an additional step that must be done until you can actual wear the equipment, which has yet to be revealed.


More details and screenshots here

Source: Siliconera