Great Weapon Master
"Cleave" plus major damage boost
Design:This design is seriously backwards. For casual users, it doesn't provide that much of a benefit, while seriously threatening to be an actual trap. For power users, it's the game's single biggest power-up.
Fun:Doing massive damage might sound fun, but it isn't fun to those left out in the cold (i.e. anyone not taking this feat, anyone that can't take the feat, and NPCs that generally don't get feats at all). Still, from a pure fun perspective, it would be dishonest to give it a bad grade.
Power:As a power gamer, the existence of this feat (together with Sharpshooter) divides martials into the have and the have nots. It's that big of a deal. Optimizing around this feat gives you much better DPR than any other minmax focus. And on top of this, you also gain "cleave" which in itself is fun and good.
Great Weapon Master
Split into two feats: Cleave and Great Weapon Master
Cleave
- Increase your Strength score by 1, to a maximum of 20.
- When you reduce a foe to 0 hit points using a melee weapon, you can make a melee attack as a bonus action during your turn.
This is the old Great Weapon Master feat with the -5/+10 part replaced by +1 Strength (as suggested by many). Because there no longer is any connection to heavy weapons specifically, the feat is renamed. Like before, Cleave applies equally to all melee weapons, including finesse ones. The way the feat only adds to Strength and not also to Dexterity is intentional.
Great Weapon Master
When making a melee attack using a weapon in both hands, you may decide to trade accuracy for momentum. You can take disadvantage on two-handed attacks until the end of your round. If you do, you add your proficiency bonus to damage of each of these attacks.
Notes:
The “-5” part is replaced by disadvantage, ensuring it can't be combined with advantage. This alone is a powerful check on minmax combos. The “+10” part is replaced by your proficiency bonus, which keeps the effect within reason for low-level characters (getting +10 at low level is a stupendous difference, and is very hard to explain within the game world. It messes too much with out of combat situations like "break this chain" or "axe this door", and it means you can't introduce hardness as an effective slow-down measure.
You still gain +6 at high level, though. Since “no advantage” is equivalent to anything between -2 to -5 but typically -3, I consider the feat to grant -3/+6 to optimized high level users. Bringing us back to where we started, though without the charop cheese!
Note that the feat no longer specifies heavy weapons. This allows you to use it with a versatile weapon if you hold it in two hands, fixing an important omission in that property's versatility!
Behind the Scenes:
In my campaign, a character with +12 reliably attacks AC 18 with the GWM damage boost, which is
way too good. The gap between +7 and AC 18 is effectively shut by advantage, top-up abilities and lucky.
As my observation to this - with disadvantage, you can't close the gap which effectively means the -5 penalty stays even if you gain advantage to negate the disadvantage. The difference is that now we've balanced the feat on the assumption you always get advantage, instead of the core assumption which is naively balanced on the initial scenario (and thus is abusable, which is the reason power gamers find it too good)
Now the feat is (hopefully) balanced for optimized high level users, which it should have been from the beginning. (That low level characters might hold off on taking this feat is not something I consider a negative)
This relies on the core rule that one disadvantage negates many advantage, so don't use this for a campaign where you've houseruled otherwise.
Feel free to shoot holes in my line of reasoning (and math), so we can improve it further
