The spiritual predecessor to the game that pretty much brought difficult games into the limelight is finally closing down its online component after nine years.
Demon's Souls, like Dark Souls after it, was built with online compatibility in mind. Players could leave helpful or trolling messages for others to read, see others' shadows if they were playing in the vicinity, and indulge in some jolly cooperation to gank invaders unfairly. The game even allowed you to invade other players as one of the many bosses.
With the online component being removed on February 28, 2018, Demon's Souls players will soon be traversing a more vastly empty world.
That means no more helpful messages, PvP boss fights, or jolly cooperation. While it also means no more gankers or backstab fishers, this definitely puts a hamper on those who want to experience (or re-experience) the kingdom of Boleteria as it was meant to be played.
So play it, while you still have the chance.