I've really only created one (three) artifacts.
One of them spanned two campaigns (in the same world).
It was a rapier. Funny thing was, it was picked up and used by a swashbuckling thief-type (Jedidiah) in a 2E adventure early on and he started using it right away. From many combats, and me finally getting tired of him asking all the time if he hit (since he knew it was magical but not HOW magical) he figured out it was +1. So he never even bothered to get it identified.
Oh, and it talked - a lot. And bragged. It was named "Vern" and when asked what powers it had, it proudly exclaims - "I can do AN-Y-THING!"
But this character never identified it, never bothered to ask it to do much, until finally, many moons later, in a nasty combat, someone got the idea to get the sword to shut up by asking it to do a meteor swarm - which it then did.
They eventually figured out it really COULD do anything - except for the problem that it was really all an illusion. But the rapier firmly believed it was all real, whatever you had it do. And there was a small (usually 1%) chance that an illusion would actually become real, which sometimes had some bizarre effects. (In one case it actually led to the introduction of a new PC - ah, fate is fickle).
What was really pathetic was just how ineffective this swashbuckler was in combat - such that once, just so he could actually get to finish off an opponent, Vern gave the illusion that he killed his opponent in one round even as he took another 12 to finish off his enemy - while the rest of the PCs had already finished off each of their foes by round 3 or 4.
So Vern was an artifact, and a rather annoying one at that. The one really powerful thing it could do was illusions - whatever you could think up, it could do, though sometimes this could have bad effects - like if you ask it to do something that really an illusion couldn't accomplish, well, you'd THINK it did it - like rescuing someone from a rug of smothering - they appear safe and sound, while they are really suffocating. That isn't too good.
It really showed how powerful it was, though, in dealing with OTHER illusions - those it could affect fully, since they weren't real either. So in one case, they were in a room where the walls were closing in - except it was all an illusion. Well, they didn't know that, but the Swashbuckler (wisdom 4, another good combination...) asked Vern to stop the walls - so then a huge wooden structure appeared that stopped them, and put a hole in the (illusionary) wall. And that illusion now is what the room looks like rather than the trap illusion.
My favorite was when there was a room in a module full of alcoves - like 100 of them, and when the party walks in, undead come out of each of them - really nasty. Except that they are all illusions. Well - the party didn't know this either, but Jedidiah still asked Vern to take care of them - so then music starts, and out of a shaft of light walks "The Cleric with no Name" - wearing a big hat, spurs, leather chaps, and a holster on each hip - and in each holster - a HOLY SYMBOL! The music swells, The Cleric with No Name walks up to stand down the 100 undead, then quick draws out the holy symbls in unision, turning them all to dust, then quickly twirling the two holy simbols in his fingers before quickly reholstering them, then riding off into the sunset (yes, the sunset was visible in the underground room, must long enough for the Cleric with No Name to walk off into it).
In the later campaign, a different party rediscovered Vern, and also determined that there were two other rapiers made, that were made to work together.
One character found one of them - it also talked, but only in the head of the owner. Its powers were different and more limited. It was also much more sober than Vern. An additional benefit of both was that when the two blades were within a reasonably close proximity to each other (a few hundred yards) they both went from +1 to +2 - and if they had found the fourth blade, they'd all have been +3.
There was a lot more roleplaying involved with the items than actual powers. I'd have to say my only experience with artifacts was a rewarding one. It was sometimes silly and Vern managed to annoy just about everybody, but they didn't want to get rid of Vern - it was a delicate balance.
