Onox: I would like to add another tip : when killing enemies (only soldiers I think, actually, at least in the first level ?) with the knife, you may sometimes get a "Mortal wound" (which looks like a mask) power-up. It permanently increases your maximum health by 5, i.e. if you pick a blue +25 health, you can go over 100. You can only do this a few times, the maximum is 120 or 125. I have only just started playing this new version, so I do not remember :)
The knife is actually a decent weapon, it is especially useful against the small beetles and leapers in the caverns or in the labyrinth in the first level, and it helps a lot conserve ammo when fighting them.
page, "Mortal Wound: Chance to be obtained when the player kills a human enemy with a single knife attack or regular arrow, restores five HP, cannot be stacked beyond 125 HP. "