Quest System Earth

John suddenly returns home after being abducted and spending 6 years on Franesh, another world. Now he's home and he's brought the "Quest System" along with him. This "Quest System" allows those with it to complete quests assigned by the system to earn EXP and even Attribute Points. Sounds cool right? Except, now dungeons are appearing all over the world and only a few people that were summoned to other worlds, and returned from them, have the power to defeat them. Amid all of these strange, new occurrences, John attempts to reconnect with his former life and his family, but that may prove more difficult than clearing the dungeons for the 17-year-old. He has the strength and abilities to clear these early dungeons alone, but he can't possibly protect the Earth from this new phenomena all by himself. Will the other few around the world with the Quest System be able to manage their dungeons? Could this be the next step of human evolution, or could it be humanity's doom?