The eternal Middle Ages.
I finally pinned down what makes me so uncomfortable in most fantasy tales. It's the passage of time--lots of it--with no progress.
A common element in fantasy is the Great Hero with his magic sword. Nothing wrong in that - but the backstory is the killer. It usually goes along the lines of 'Ten thousand years ago, a Mighty King rode his horse, led an army armed with swords, bow, spears and axes into battle and had the shit royally kicked out of him. Now his vengeful descendant (or the Bad Guy reborn, more often) wants to take over the world and make everyone suffer'.
Okay. I'm fine so far.
BUT if ten thousand years have passed, why is the hero STILL riding a horse, STILL fighting with a sword, STILL wearing leather armour?
Why doesn't he have an enchanted tank, or a blessed F-15? At the very least, a magical Uzi.
There is no gunpowder. No guns. No cannons. Not so much as a trebuchet. No internal combustion engine. Not even a steam engine. Few wheels, if it comes to that.
Now, this is a world that's been at war for most of its long existence. You'd think at least one of the people in it might try to improve their chances of winning. Wars accelerate development of things like jet engines, rockets, radar: anything that would give an edge over the enemy.
In fantasy? Nothing. The entire world is populated by unthinking, uninventive dolts. The bad guy deserves to win. He's the only one who's made any effort. He's the one with the war machines.
You can have magic, raising the dead, mysterious gods, all of that, but please, please let your world invent things. Instead of a flaming torch, just once let's see your elf pull out a flashlight. Maybe just a folding pocket knife? A pair of pliers? Scissors?
Anything to prove the world you've created isn't utterly stagnant.