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.
Fetish Fuel: The way Kayako claims some of her victims (ie. enveloping Vanessa in her hair, amongst other examples).
Fridge Logic / Plot Hole: Where on Earth did Naoko get hold of Kayako's blood from? (Unless it's just a substance that represents it, or something.)
Seeing how Kayako is covered in blood, it's only a matter of getting close enough without being killed.
Hell Is That Noise: Kayako's death rattle. Enough said. Also, the sound of a cat's meow has never sounded as creepy as it does in this series. Not to mention the sound of Naoko's breathing, post-death...
This may also be the reason why the death of Mrs. Davies was cut from the second movie - although pretty shocking in nature, it is visually a little too similar to the death of Yoko from the first movie.
Les Yay: There seems to be some very subtext-y moments between Allison and Vanessa in the second movie.
Not to mention the way Kayako seems to be all over her (usually female) victims when she kills them (Karen and Dr. Sullivan, for example - not to mention the way she clings to Karen's corpse after she kills her). A little bit of Foe Yay, perhaps?
The scene in the second movie where Aubrey goes to Karen and Doug's apartment the day after witnessing Karen's death. Aubrey glances around the apartment, eventually looks over Karen's collection of framed photos, and breaks down sobbing as her sister's death suddenly hits her.
Max's reaction when he finds out that, while possessed, he killed Naoko. After the possession wears off, the poor guy just looks so broken and confused... then the realisation just suddenly hits him and he starts sobbing on the floor.
Uncanny Valley: Kayako is given an appropriately creepy walk via a combination of stop-motion effects and Takako Fuji and Aiko Horichi's talents at performing creepy, jerky movements.
Also, in the third movie, Naoko has an incredibly unsettling walk after her transformation into Stringy-Haired Ghost Girl, thanks to her knee being broken prior to her death.
The Woobie: A good chunk of characters, but especially Allison, Jake, Aubrey and Rose.