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.
Big Lipped Alligator Moment: The scene mentioned under Foe Yay is specifically stated by the author to be there only to please the ZADR fans. It is never mentioned again, and in fact, the following chapter has a flashback showing what really happened, which has no Foe Yay at all.
In fact, that chapter could almost be considered a Bizarro Episode. It does get mentioned briefly the following chapter, but aside from that, it just completely comes out of nowhere, and the plot seems closer to a canon episode, whereas most chapters leading up to it had been increasingly more serious.
Fixer Sue: Nick, the narrator, is called a Fixer Sue (by Johnny the Homicidal Maniac , to be exact). It should be noted that until the end, his efforts were unsuccessful, and while he makes friends with most of the canon characters, he also gets his fair share of crap dumped on him too.
Foe Yay: There’s a “happy ending” scene at the end of “The Terror of the Pies” when Zim and Dib just finally break down the walls, finally satisfying all the fans who were waiting for a ZADR moment.
Fridge Brilliance: The fate of the Infinite Energy Absorbing Blob once you piece the clues together.
Jerk Sue: Gaz, without a doubt. She’s almost always off in her own little world and rarely helps for the benefit of anybody but herself. The reason WHY she acts like that is surprising though.
Mary Sue: Nick, the main character, is undoubtedly one. This character makes other characters out of characters. For example, he convinces Zim to completely go against his previous characterization towards Dib. This character is always at the center of the action, being a mediator towards all of their actions. Any flaws this character has are minor and irrelevant.
Debatable. Nick tries frequently to get Zim and the others to change but the change almost NEVER sticks. Usually whatever good Nick does is undone by the end of the chapter.
Nightmare Fuel: The chapter in which Tallest Miyuki and Spork return is FILLED with this.
Relationship Sue: A deliberate Mary Sue who only wants to make Zim go gaa-gaa over her, through fair means and foul, the character Relationship Sue has unrealistically-colored eyes, beautiful features, can turn into an Irken, magical powers, enormous breasts, etc. She is gleefully squished by Gaz in an enormous monster truck, yet she comes back 18 chapters later...and is now in love with Dib, hoping to kill ZIM off. The constant pain and humiliation she endures throughout the rest of the chapter is an all-too-clear take on what the author thinks of poorly-thought-out eye candy-esque fanservice characters.
Also, for people who had followed the story from the first chapter, the realization that it was finally over was like this, especially taking into account how awesome and heartwarming the ending was. This troper was actually in tears when I finished reading it.