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.
Fandom Rivalry / Friendly Fandoms: With Doctor Who. At first, there was some unease over the fact that the show was basically created to ride on that show's popularity, but it dissipated when people came to realize that Primeval was actually quite different, and told a respectable story of its own. Many people like both now.
Fanon: A surprising number of people believe that Jess is either Lester's daughter or his niece.
Hell Is That Noise - In the series 1 finale, the team carry an oscilloscope which can detect the high frequency calls made by the bat-like future predators. Whenever it starts to bleep, you know you're in trouble!
Ho Yay: Nick and Stephen are pretty well suited for this. Especially given that Stephen's fairly quiet and has known Cutter for roundabout 10 years and thus has an interesting tendency to communicate with him via long, meaningful gazes.
Connor and Stephen in 1.3, lampshaded by the latter. In fact, Connor was just asking if Stephen really had a girlfriend, because he had a crush on Abby (who was interested in Stephen), but it ends up sounding like something else.
Moral Event Horizon: For Helen, her MEH is either when she kills Nick, after he came back to rescue her from a burning building or when she kills Christine which shows that while she's usually willing to murder many for her means before, but this was arguably the one point she clearly favored sadistic torture over just getting the job done quick, or her plan to wipe out humanity before it even starts
Thankfully, this sound effect was eradicated from the show after Series 2.
Narm: In the last episode, Matt says "Nothing can survive out there, except for those ugly freaks".
Matt's knife fight with the Treecreeper in the Cretaceous was also pretty silly. Could be Narm Charm if you find the scene awesome.
Hearing Nick Cutter shout can rub off as this, if only because we're so used to him being quiet and brooding.
Nightmare Fuel: Any and all appearances of the future predators. They've done a very good job of avoiding Villain Decay, despite the fact that they're clearly not impossible to kill.
The dodo parasite from 1.4. For that matter, the fungus creature from 3.5.
The Mer creatures, particularly their angelic singing. Cutter speculates them to be the descendants of humans.
Pretty much any creature qualifies for either this or regular Nightmare Fuel for someone.
Seasonal Rot: Season 3 is generally considered by fans to be the worst-written of the series, particularly the last three episodes. But most of them agree that it picked itself back up with 4 and 5. Some however think the opposite, in that Series 4 and 5 are the worst.
The Scrappy: Matt (with a side order of Creator's Pet), half an hour into the first episode of the Revival and he already is hated by some for being a smug git. Then again, his background is both false and was created specifically to appeal to the ARC recruiters, so he's supposed to seem like a Creator's Pet.
By the end of the series he's become a much more sympathetic character. We actually feel sorry for him when His future self pops up ruining his happy ending.
Jack, Abby's brother. He constantly stuck his nose in his sister's business and wound up getting himself trapped in the future. Even after Connor, Becker, Danny and Abby head into the future to save him, he just complains about how long they took. Eventually he realizes all the trouble he's caused and is Put on a Bus.
Hell, the title sequence. Even moreso in Seasons 4-5.
Seasons 4 and 5note Which replaced Framestore with acclaimed commercial effects firm The Mill got a bit of a visual touch-up with a more HD quality, in order to regain audience attention.
The Woobie: Cutter is the most well-known example, having believed that his wife was dead for 8 years before meeting her again but finding that she'd become Ax-Crazy. Later he tries to get over it by forming a romance with Claudia Brown, but then she gets erased from history and he spends the whole of season 2 trying in vain to find any trace of Claudia in Jenny Lewis, her double. And if that wasn't bad enough, he loses his best friend and finally is killed by Helen in Season 3.
After losing Danny, Connor, Abby and then Sarah, whilst on a mission to rescue the former three, Becker certainly qualifies for this. He's practically in tears in the first episode of the extras on ITV's website.
Connor and Abby after their year in the Cretaceous.