Of +1 Swords, Their Eradication and Their More Glorious Brethren
"'Take care, you dunghill cocks! Notice the fate of your fellow! He died by the power of my magic blade, which is of inexorable metal and cuts rock and steel like butter. Behold!'"
It's been discussed in discord, blogs, and elsewhere. It's almost a meme now. Plain old +1 magic swords are boring and become disposable. Other have tried to make them unique and interesting. I'm probably repeating ideas others have already thought of, but here's my attempt with a bit of clickbait.
Heirloom Weapons
I am wearing a cape and hold a [newly puchased antique] sword in my hand, a straight sword three feet long in a carved wooden sheath wih a brass clip.
No +1 weapon is magical. They are weapons of fine construction1 passed down between generations or as an honor for some great service. Heirloom weapons provide a bonus of +1 to hit and +1 to damage. They cannot harm creatures that require magic weapons to hurt. While an heirloom sword may be finely balanced and the hilt reliable, they can be damaged and destroyed like any other mundane weapon. They are probably pretty and nice to look at.
Most have a history or a fancy (or goofy) name. You can't buy an heirloom sword at the local blacksmith or even from the armory in a big city. You might be able to give a tidy sum to that wierd guy that sells weird stuff down in the sewer, but he might be selling you a fake. Maybe you found one on a corpse. The original owners will probably want it back.
True Magic Weapons
A Mighty Guard Of Fire With Two-edged Swords Flaming
Magic weapons typically have +2 or better bonus to hit and damage. Some grant additional bonus against certain types of foes (giants, dragons) or under specific conditions (light of the full moon).
Magic weapons do a minimum damage equivalent to their bonus (a +2 guisarme might do d8+2 damage, but all damage rolls of '1' are treated as a roll of '2')
Magic weapons can shed very small amount of light (only enough to read text, inscriptions, details within 6") when held in some form of a non-combat grip. It's not anywhere as bright as torchlight and you won't be able to see the door a 10' room with it. Different weapons glow different colors and will probably impress the rubes.
Magic weapons are required to damage some types of unnatural creatures. Make it fun and make more creatures in your usual manual of monstrosities require them.
Each magic weapon has a name. It may have a funky name like 'Glamdring' or something more colloquial like 'Foe-hammer'. Maybe both, but it has a name. A weapon's fame might draw undue attention. Beware of thieves and unscrupulous innkeepers if you carry a distinct arbalest - they may want it for reasons beyond the silver inlay.
Magic weapons can be still be damaged by extraordinary means (dragonfire, the strength of a titan), but rarely completely destroyed. They can be rendered functionally inoperable (broken blade, damaged head, cracked shaft, etc) but be used as an improvised weapon and retains the ability to harm monsters requiring a magic weapon to hit. Special artisans (old smith living deep in the woods, a certain crafting kind of wizard) to repair it. With the proper materials (and a tidy sum of coin), the repair typically takes one week.
Each magic weapon has a minor power (the higher the plus, the more potent the minor power). d4caltops has a fine list if you need ideas
Some magical weapons are sentient and the greatest of those may have demons, spirits, or human souls bound into them. (Refer to the AD&D Dungeon Master's Guide or another great d4caltrops blogpost until I write my own post). When in doubt, assume 25% of weapons +3 or greater are sentient and 50% of such swords. Those sentient +3 weapons are empathetic, +4 weapons have speech, and +5 swords have speech and telepathy
Weapons of a +3 and greater bonus are made of weird alloys beyond just steel (meteoric iron, aurichalcum, adamantite or mithral alloys).
Each magic weapon has at least one distinctive mostly ornamental feature (My kingdom to have Abulafia back!) - inlaying, enscribing, etching, excesively ornate quillons or hilt, decorative patterns, obscure leathers, set with semi-precious stones...
Some greater magic weapons can have a single enchanted gem, runes, or talisman embedded in them for additional minor powers. Only special artisans can embed, remove or replace these.
Some games call items like this "masterwork", but that's a boring name and they seem to be available from any above average smith for a small sum more than the run of the mill equivalent weapon.↩