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.
Gamers and gaming in "Hitting for the Cycle". For the love of all that is holy...
Subverted in, of all places, the episode that dealt with actual circus freaks. The freaks are the most sympathetic characters in the episode, are not portrayed as pathetic or as people to be looked down on, and the killer turns out to be by far the most "normal" out of all the suspects.
In at least three different instances, sex offenders were "outed" to their neighbors (and thus had their lives ruined by the CSIs) despite fact that in all three cases, the people involved had a) served their jail time and were now leading clean, unoffensive lives b) were only tangentally involved in the cases, if even that, and c) police investigators aren't supposed to give out information on suspects to the general public anyway regardless of what that information is, as doing so until a conviction occurs is a serious civil rights violation.
When Grissom returned in a guest spot in Season 11, and the rumours that he'll be back in Season 12 for Catherine's exit. Although he didn't return, the PT Bs feared it would take too much focus off Catherine.
Anvilicious: The episode centered around internet bullying, though possibly a case where this needs to be brought to the public eye but it does get a bit egregious when Nick basically tries to say anyone who ever looked at the mocking videos, even if they did nothing about it or thought it was in bad taste, deserved to be put to the court system.
Base Breaker: Sara is either one of the most compelling and woobieish characters on the show, or just plain crass and annoying.
Ray Langston...either he was a great character or Creator's Pet and really overused and given too much to do for a CSI 1.
Broken Base: Dear Lord. Some fans insist the show Jumped the Shark after Season 5. Others say it happened when Grissom was shown in bed with Sara in the season 6 finale. Some say it didn't happen until Season 8/9 with Warrick's death and Grissom leaving. Some declare Season 11 the worst due to it dragging out the Ray/Haskell storyline. Ray leaving and two new characters entering is only causing more divides in the fandom. Recent events in the (mostly off-screen) relationship between Sara and Grissom appear likely to cause even more division among fans.
Mandy and Cameron Klinefeld from season 4's "Assume Nothing" put the "unholy" back in Unholy Matrimony. A married couple united by a shared sexual fetish for rape and murder, the pair operate by abducting other husbands and wives, sexually torturing the women while making the men watch, with the ultimate goal of forcing them to Mercy Kill the women they love. They promise the husbands they can go free if they do this, but they're lying.
Season 12 Arc Villain Laura Gabriel is a ruthless arms smuggler and Big Bad Friend to Catherine Willows. Playing a meek and submissive wife to her sleazy private military firm head husband Mark, she uses this false personality to deflect blame off her and onto him as she funnels his company's weapons to The Mafia and The Cartels. When the investigation starts getting too close to the truth, she hires employees of the company to murder her own lawyer and all of his staff; following this, she kills the assassins and burns their bodies beyond recognition in order to fake her own death and that of her right-hand man. She intended for an enraged Catherine to summarily execute her husband, and also placed a contract on Catherine herself to clean up the last remaining loose end, not caring for her old friend in the slightest.
Creator's Pet: Ray Langston. Many fans either dislike him or thinks he's So Okay, It's Average, yet in his run he had three season finales, the 200th episode and two season long serial killer arcs dedicated to him and his problems.
Ensemble Darkhorse: Greg and Hodges in earlier seasons; when they were promoted to main characters the other lab rats got the same treatment, with Archie and Mandy in particular being well loved by the fans.
Fridge Brilliance: In the 300th episode, "Frame By Frame", Sara comments that Gwen might still be alive if they had solved the Darcy Blaine case fourteen years earlier. It later turns out she's right, but not for the reason she thinks. If they had solved the Darcy Blaine case, they would have discovered she had faked her death, negating the need for Gerry hiring Gwen and Emily to break into Jack's mansion to steal the evidence of such. Gwen and Emily might have worked out their boyfriend issues more peacefully in another environment.
Harsher in Hindsight (Or Foresight, considering there was at least 5 hours between the conclusion and the show's airing): An episode about a very troubled person shooting up the LVPD (3 dead including the gunman, a teenager; additionally the person who manipulated him into shooting was arrested, at least a dozen wounded) airs the same day a very troubled person shoots up an army base (4 dead including the gunman, over a dozen wounded).
Ho Yay: Nick and Greg. In fact, such a pairing has a large following, especially due to the subtext that occurs in their interactions.
The issues in Grissom and Sara's relationship and the recent revelation about them have fans yelling it again.
Padding: The video games REALLY make you work to match fingerprints, DNA, and chemical samples.
Retroactive Recognition: A lot of secondary guest stars eventually found fame after their appearance on CSI: Crime Scene Investigation. Rainn Wilson and John Krasinski both had guest spots before their own hit show, with Wilson having a memorable bit in one of the more popular episodes ("The Strip Strangler") as a possible suspect. And CSI NY 's Carmine Giovinazzo was a guest star on here before becoming a regular on the spinoff series. But, Word of God says the guest appearance wasn't an influence in casting him. A.J. Buckley, also from CSI NY, appeared on this show before becoming a regular on the spinoff.
Norm was the killer (sort of) in "Dog Eat Dog." The best example, however, is Eric Stonestreet as Ronnie Litra, the lab's questioned documents expert, who disappeared without explanation around the middle of Season 4... and is now quite famous as Cameron.
The Scrappy: Kevin, "Hitting for the Cycle". How on earth did he get hired? He bites the dust at the end of the episode.
Seasonal Rot: Happens with nearly any Long Runner. While not bad in its later years, the show received a lot more press, ratings, and critical acclaim in its first few seasons (even earning a few Emmy nominations). One could make a case with show growing stale as early as Seasons 6/7, but it was likely Grissom's departure in Season 9 that really accelerated things.