These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Critical Research Failure: The GURPS book, set after Soulblighter, has several references to The Deciever fading into the background and refusing to share information after the battle with Shiver. That's probably because he died in that battle (see Taking You with Me).
The Trow iron warriors in Myth III. Remember how the Trow in the first two games were capable of killing several of your best units even when surrounded, were too fast to outrun, but only showed up in small numbers so it was a fair challenge? These guys are kind of like that, except armored like a tank and carrying a Big Freaking Hammer, which liquefies several units with each blow. They also have a ton of HP and don't turn to stone until it's fully depleted. You also have no special abilities or giant units of your own to counter them. They frequently come at you in pairs and there are levels with more than ten of them. Ironically, the only way to beat them is to exploit the equally broken AI, which doesn't realise that Trow now move, turn and attack too slow to ever catch or hit some units and will gladly run in circles after a lone Heron Guard while your archers and dwarfs rape them ever so slowly. Worst of all this is how the developers intended you to beat them. Way to completely take the fun out of the game.
The Tain makes fighting meaningless, though it only lasts for half a level. Why it's not used again later is anybody's guess. It is so overpowered that the rest of that campaign, after the only enemy that can counter it is dead, happens offscreen.
The Tain isn't used again because it summoned an army of mind-controlling extra-dimensional spiders that the Dwarves who created it died to stop.
Narm: Myth III often lapses into this thanks to some hammy voice acting in contrast to an otherwise fairly dark and serious story and cutscenes that feature characters making silly gestures and not moving their mouths while speaking.
They Changed It, Now It Sucks: The main complaint about Myth III, aside from the horrendous number of bugs, was that it just doesn't feel like a Myth game with the perspective switch from the desperate average soldier to the fearless conquering hero. The goofy looking cutscenes and drawings, bland level design and addition of magic-users from races that weren't supposed to have the intelligence for it didn't help either. Turning the Trow from the iconic fast and deadly juggernauts into completely brokensluggishretards and then making them the main enemy for several levels in a row was the last straw for most fans.