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.
Complete Monster: Marcel Janvier, AKA The Chameleon, runs several cartels from behind the scenes, and the closest thing to an MO that he has is that he acts as the driver. He kills people by incinerating them in their cars and plays a dangerous game of "hide and seek" where he forces people to act as him to lure them to dead ends, which often results in their deaths in the process. When infiltrating the NCIS, he murders and assumes the identity of a police officer to infiltrate the operation to capture him. In his proper debut appearance, Janvier set up a family of arms dealers to be killed by the police and car bombs Agent Lauren Hunter before allowing his own arrest to blackmail the NCIS by threatening to inform Iran of a US spy working in Tehran. Marcel Janvier cares only about his own profit and has no regard for human life. With one of the highest bodycounts in the NCIS franchise, The Chameleon is one of the most monstrous villains the franchise has to offer.
"Sam sees the glass as half-full. I see the glass as half-empty, that's why we make such a good team. Kensi, on the other hand, drinks straight out of the bottle, Nate wonders why it's a glass and Eric usually breaks the glass by putting his feet on the table."
After Eric explains how he stopped the release of a terrorist's threat video
Foe Yay: Hetty pretended to be Kohl's wife for so long she acknowleges it's the closest she's ever been to actually being married.
Germans Love David Hasselhoff: In Portugal, most promotional materials and ads for the show focus near exclusively on Kensi (played by Portuguese actress Daniela Ruah) to the extent that you'd think she was the main character.
Harsher in Hindsight: Kensi comments to a terrorist suspect in Season Four (Chosen One) and that if she was being held by jihadists, her only right would be to have her head cut off. Come Season Five (Zero Day and Spoils of War), she is indeed captured by the Taliban while on assignment in Afghanistan. As revealed by deleted scenes (Spoiles of War) that is exactly what her captors threatened to do.
Hilarious in Hindsight: Everyone's mockery of the idea of Nate in the field. Considering how awesome he is in the field now ...
Hanna: I really look forward to having Dom as a partner. Callen: You'd miss me. I complete you.
This immediately after Callen asking Hanna if he had a history with their suspect, and Hanna responding with "We weren't dating, if that's what you're asking."
Kensi once asked Hanna how long he and Callen had been married. At what point does it stop being subtext?
Probably one episode before that when Hetty suggests Callen take out the attractive treasury agent, and then take Sam out the next night so he "doesn't get jealous."
The hoyay between Sam and Callen has just been increasing over the past few seasons... or at least, the implications on Callen's side have, culminating in the 4th season finale, where The Chameleon singles out Sam as his target to hurt Callen with, going so far as to refer to him as Callens "beloved partner".
Iron Woobie: Hard not to see Callen as this after everything he's gone through.
Special Effects Failure: While the practical effects of the show are incredibly impressive, the CGI effects leave much to be desired. Justified in that it is a TV show, not a movie and thus only has a small CGI budget.
The Scrappy: Henrietta in later seasons for a variety of reasons, such as purposefully withholding information from the team that could help their case and manipulating the team on multiple counts for her own agenda. Nearly getting Kensi killed in Afghanistan didn't win her points with the fans.
However, with the debut of the sixth season, she has subsequently regained a lot of love from the fans. Whether or not she is Rescued from the Scrappy Heap remains to be seen.
Too Soon: Averted in "Neighborhood Watch": in the wake of the Trayvon Martin shooting a movie changed its name to just The Watch and a reality series of the same name about watchmen was apparently canceled; not this episode. A lot of people get shot in a gated community in a sunny state, though none of them were black (a few wear hoodies, though).
Actually, make that Deeks full stop- he has a tendency to look so utterly broken and exhausted even when he's still going that it's almost like he's got a giant flashing neon sign around his neck that says 'I'm A Woobie'.