To me, "brutal" means that it is easy to get killed, and that dying is punished. Which is exactly what happens in the game.

Didn't keep your foods up? Too bad, you're dead.
Didn't manage your stamina properly? Too bad, you're dead.
Didn't refresh your Rested buff, especially if also Cold? Too bad, you're dead.
Were overconfident in your combat abilities? Too bad, you're dead.
Didn't look where you were going and fell off a cliff? Too bad, you're dead.
Didn't think before taking on a difficult enemy or a group of enemies? Too bad, you're dead.

Basically:
Weren't prepared? Too bad, you're dead.

Dying punishment, of course, is dropping the entire inventory and losing skills. The former can cause a huge problem if you die in a spot that's hard to reach.