Deadlier. Players have guns and better path finding and aim.

Surviving the environment is sometimes just as hard, you can break bones and then you are toast if you can't drag yourself to a hospital without dying, you can freeze to death, die of thirst, starve, go insane...
And the crap storage and picking up items and controls systems make it even harder. Not to mention the fact that zombies can climb ladders and glitch through walls and doors, and sometimes you can literally kill yourself by closing a door on yourself accidentally.