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.
Badass Decay: Hordriss. When first introduced, he's a dangerous character with an agenda of his own; not as powerful as either Big Bad, but definitely a force to be reckoned with. By the last couple of series, he routinely falls for every simple trick that Lord Fear or Lissard use on him and is only still on deck because of dungeoneers showing up in the nick of time to save him.
Growing the Beard: It's widely accepted among fans that despite its insane difficulty in comparison to what came later, Series 3 was by far the best of the show's run.
Nightmare Fuel: The life force meter. It took the form of a knight's helmeted head for the first 5 seasons. As the Dungeoneer gradually lost health, pieces of the knight's helmet broke off and flew away. Okay, not so bad. But then when the helmet was completely gone, the skin of the knight's head began peeling away to reveal a skull underneath, as the face goes through a series of suitably shocked and horrified expressions until it no longer has lips to emote with. And after that, the skull itself cracked and fell apart, the remaining chunk of it flying towards the camera to leave just the eyes which then rolled out of the screen one by one. BONG! "Ooh, nasty."
Gundrada the Swordmistress from series 4. Quite a fun character and helpful to the teams but her ridiculous (and very annoying) voice earned her plenty of hate from the viewers.
Snapper-Jack from Series 8, mostly due to the poor execution of the character, which makes him look less like a man with a dragon-like creature in place of his arm, and more like a really bad ventriloquist act.
Seasonal Rot: Series 4-7 are generally regarded as a step down from, at the very least, Series 3. Series 8 is something of a Base Breaker, as some fans appreciated the return to the format of Series 3, though many feel that it was poorly executed and suffered from decisions such as allowing the last two teams to skip straight from Level 1 to Level 3.
What an Idiot: A team was once told to not wake up the dragon and to use a spell first, and an advisor then insisted they wake the dragon up first.