The hardest content besides from raids and the Trials Of Osiris is the Grandmaster nightfalls. Grandmaster Nightfalls cap the player at a cetain level so the enemies will always hit harder than you do a single bullet or rocket from an enemy will wipe your team if you are not carefull. Below there is a video showing what a grandmaster nightfall is like be sure to check it out. The video on the left below is one of the newest strikes that was added on febuary 22nd. It is called birthplace of the vile this is done on the hardest difficulty possible.