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.
Creator's Pet: The Gnome race as a whole. They seem to have a major role in almost every expansion and they get more attention than most of the other races put together. If you play a Wood Elf or Halfling or Sarnak or some other unfavored race and want more content? Tough! Have some more wacky gnome hijinx!
Demonic Spiders: The "key mobs" are these for people who like to solo zones. They have one ability called Mandate, which stops you from targetting the mob, stops you from healing (including curing the ability off yourself), and if you do try and cast an spells that don't need a target, such as an AoE, it will send you flying around the room. It doesn't help that some of these keymobs are near named mobs, and, if they aggro, they can spell your doom.
Player Punch: EQ2. Discovering Erollisi Marr's death. Though the punch is severely diminished now that we know she's back.
Scrappy Mechanic: The way The Scavanator would despawn after he wiped a raid made it impossible to really practice working on him.
That One Boss: Dozens of them, seriously. In an effort to make the game more challenging for the ever-increasing-in-power player base, boss mobs come equipped with debuffs of ever-increasing-nastiness.
A good example, although not the only one by any means, is Pawbuster in EQ2. An level 84 "Epic x4" Drolvarg. Basically, there's a grate in his room. Pawbuster occasionally does an attack where he smashes the ground. He has to be placed exactly so he hits certain bolts when he does this. While all this is going on, he has a regular area-of-effect 50 second stifle (mutes/disables spells/combat abilities), and a nasty DoT (damage over time).
The Pawbuster ends in one of the most satisfying ways ever conceived in an MMORPG though. Once you wear him down just enough, a player pulls a switch and drops him into the whirling blood-soaked fans right underneath him.
Bosses get steadily more ludicrous. The boss of the Destiny of Velious expansion, the Statue of Rallos Zek. First you have to pull him about an in-game mile down a long slope. You have to stay out of his reach and ranged damage him, because otherwise he'll wipe the raid. Periodically he anchors himself and releases an AOE, you have to be out of range or you get flattened. As soon as he's done he "memwipes" and the tank has to grab him before he attacks the raid. You have to gradually drag him backwards, across a ridge running across the floor that messes up line of sight and exists only to be annoying. While doing all this you also have to be constantly burning down the warboars he summons, which "target lock" players, forcing them to target the warboars and making it hard to heal and attack the statue. You have to drain him to 30% health and run him to a fountain, at which point a red tornado spawns, that you have to kill (but you can't kill it until the Statue has been dragged away from it, otherwise he wipes the raid). Once tornado #1 is down you have to drag him waaay across the room to the other fountain and make another red tornado spawn, then kill it. Oh, once the statue goes below 50% of its health, each raid death heals it by 5%. By the way did I mention that this is just the "easy mode" version of the right? Because it is.
That One Sidequest: In EQ2, the Roekillik quest line. It was released to hype the Kingdom of Sky expansion pack. It is still outlandishly difficult even for a lvl 90 character, and the rewards, well, completely suck. No one does it anymore.
They Just Didn't Care: Is there any other explanation for why almost every single change they make to EQ2 in the name of "streamlining the experience" actually involves removing content and dumbing down what's left? The most recent one made the rewards for any new character in any of the newbie zones... absolutely identical. That armor with the arctic-conditions protection texture they made for their big New Halas patch? Yeah, now characters in the (tropical) Timorous Deep get that armor. Why was weight removed from the game? Why does every expac simplify the way stats work?
At this point in time, none of the original EQ2 developers still work on the game, and the ones that do now have admitted that they don't care at all about the original Qeynos/Freeport setting.
Tier-Induced Scrappy: Every time a new expansion drops, there's usually at least one high tier and one low tier. Oftentimes the formerly high tier gets nerfed into low tierdom. For example, in Sentinel's Fate Defilers were highly favored over Mystics because of stronger base heals. Then in Destiny of Velious new AA lines both pulled Mystics back in line with Defilers on healing and made them a decent DPS class as well, leading to Mystics being the more favored.
Raiding has its own set of Tier Induced Scrappies. Berserkers, Monks and Wardens in particular are rarely wanted on raids, whereas wizards, inquisitors and both shamans can get raid slots with great ease compared to other classes.
Unfortunate Implications: Some people felt this way about white people and black people being two entirely different races in EQ1. Whites were regular humans, while blacks were tall slender universally intellectual people called "erudites". In EQ2, SoE changed it so all humans, as well as half-elves and barbarians, could have various skin colors including shades of dark brown. Meanwhile, the erudites were changed to have skin in various shades of gray. They brought back the original style erudites in Sentinel's Fate, though.