Have I actually laid out what my issues with the weapons list in 5e is? It's both boring and long, with obvious traps in damage and functionality, and somehow also lacking in anything resembling interest. If you want to do a big long list of weaponry, you can do better by looking at one of the Warhammer 40k weapon lists, with all of its modifiers and finnicky bonii, or you can look directly at FantasyCraft, which takes great pains to make each weapon type distinct through the liberal use of feats and class features.
5e doesn't do either, which is why I always want to get rid of it. 5e isn't really a game about whether you should bring a sword or an axe or a spear, and I kind of want it to be.
So here's a little something inspired by much-maligned weapon speed rules in 1E.
The basic idea is that, in a melee, those with longer weapons get to strike first. They always make the attack roll first. Unfortunately, longer weapons also need more space to operate.
There's also a difference between 'thrusting' and 'swinging' weapons.
Thrusting weapons attack in a straight line, can skewer through enemies to strike enemies behind them, and can pin enemies to walls.
Swinging weapons, like axes, can cleave through all enemies around them, push enemies away from them in any direction. Unfortunately, if you try and use a swinging weapon in an enclosed space, you suffer disadvantage on your attacks.
Swords, uniquely, can both thrust and swing. They are much more expensive than any other weapon type, however.
So now real-world tactics can apply. If you have a spear, you'll want to line your enemies up behind one another, and fight in narrower corridors where your superior weapon length lets you keep them somewhat at bay. A superior fighter will still overcome you, but at least you have the first strike.
If you're operating mostly on your own, or in disorganized and chaotic melees, you can swing your axe with reckless abandon in a big open area. But tight, confined areas are not great for you. You're at your best with lots of room to manipulate your foes.
If you've got a sword, you can thrust in tight quarters or swing in more open ones. It's not as long as a spear, of course, but you can't have it all.
So now there are tradeoffs and benefits to each type of weapon, and different kinds of warriors are going to want to use different types of weaponry.
I'm still working on how to use skewering, cleaving, pushing, and pinning in 5e. I'm thinking as a bonus to when you beat your enemy's AC by more than 5, you get to use one of your weapon's benefits. So if your enemy's AC is 15 and you roll a 21, you can skewer behind them with your spear, or force them backwards with your axe (possibly off a cliff or into a fire, or whatever). Cleaving lets you hit multiple foes at once. Pinning lets you keep your enemies in place.
Larger enemies need more space, but also always attack first. A giant is going to need a lot of room to swing its club around. Creatures with natural weapons probably don't need a lot of room- that troll sure is dangerous in a cramped warren...
Monks should just flat out be able to strike first, since they're movie martial artists and one has to imagine in a world full of swords they've practiced how to step into a guard or whatever. If you have a different conception of monks in your world, feel free to change this. Maybe they strike like a shortsword. Up to you.
None of this is playtested. Use at your own risk.
This also works pretty well with another system I've been working on, and something I've posted here before:
Weapon Damage by SizeSo in this scheme, one-handed weapons do 1d6 damage and two-handed weapons do 1d8 damage. If you're a Fighter, Barbarian, Ranger, or Paladin (the warrior-type classes of 5e), then your one-handed weapons deal 1d8 damage and your two-handed weapons deal 1d10.
Light and/or Finesse weapons drop the size down one die, so a two-handed finesse weapon wielded by a non-warrior deals 1d6 damage, and a Fighter's two-handed hammer toss deals 1d8 damage.
Light weapons can be thrown, and Finesse weapons allow the wielder to choose between Strength and Dexterity when making melee attacks.
Weapons are further differentiated by their critical effects:
Swords and daggers critical on 19-20.
Axes step up their die size on a critical hit (so a two-handed axe crit by a Barbarian deals 1d12 damage)
Blunt weapons stun their foes (DC equal to 10+damage). The wielder may also optionally push / knock that enemy prone.
If you combine the two, I feel like you've got a pretty robust system.
As a DM, you'll need to be fair with adjucating when various weapons will or won't work. Tight spaces can mess with a sword, but being surrounded is bad news for a spear. People can hide underneath things if a reaver with an axe is coming at them, and goblins might retreat into tight warrens to escape a barbarian.
As usual, let me know what you think. I may not respond to many, but I read every single one of them, and it always makes my day to know what people think about what I'm working on.
I'm going to try and be better about sharing what I'm writing about instead of churning endlessly throught Notepad++ tabs, deleting everything, and starting over like I'm accustomed to doing... if for no other reason than maybe sharing some of my ideas can get them to stick a bit.