A script that would allow the player to do more damage to humanoid npcs of the vanilla Skyrim races (eg. bandits of varying races, etc.). This, in turn, would make it so that monsters, even those added by mods, would be stronger by comparison.
The reason? At a higher level, giants are as strong or weaker than high level bandit characters, and this should not be the case. A simple script that increases a player's damage amplitude against enemies of the vanilla races would fix this. A player could then expect reasonably easy humanoid enemies on the harder difficulties and drastically more difficult enemies of the animal/creature/monster variety. Also, if possible, taking less damage to humanoid npcs (melee) would be much better too, as a forsworn sword-slash should never be as powerful as a giant's swipe.
The only caveat worth noting here is that Orcs MAY NOT need to be affected by this script as they are green and brutish, and I reckon them to be worthy of a stronger combat presence, by personal taste. Vampire races should remain strong as well.
P.s., I understand that there are mods that make monsters/animals stronger, but they do not always affect creatures added by other mods. In other words, If I were to use a mod that increases monster health for example, I could expect my vanilla trolls and giants to be juggernauts, but my flamelurkers or ancenstral troll (added by MonsterModV13 and BoT, respectively) may remain as weak as they were before. A script that recognizes the race of the npc enemy could, instead, simply determine if the said enemy applies for a damage amplification or not, and modifying the vanilla races in this way could prove to be maximally compatible with all other mods.