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.
YMMV: Walking With Dinosaurs
Critical Backlash: From the general scientist/paleontologist community, but mostly from those to whom scientific accuracy is Serious Business and any amount of speculation is intolerable. One such person infamously labeled the show's paleontology consultants "prostitutes" for "selling out" their knowledge to a fancy TV show.
Narm: In Walking With Monsters. For all its hunting prowess and deadliness, the famous crested mammal-ancestor Dimetrodon looks pretty damn goofy when it's running.
Justified in the fact that every land vertebrate at that time period ran more or less like that, and the 10-feet one was likely to outrun everything else. And its following evolutionary stage (the gorgonopsid) loses its "clumsiness" altogether.
The final fate of the tyrannosaurid family at the end of "Death of a Dynasty" rather comically clashes with the grimness of the scene. To elaborate: The mother died from her leg wound, with the surviving infants clustering around her body. Then the meteor shockwave hits. The babies get suck up by the wind and zoom away, followed by the mother's corpse being lazily dragged after them.
Special Effect Failure: Even these shows weren't immune to this: the most common goofs are CG clipping errors (like when the mammoth's trunk "merges" with its tusk), wires from the animatronic models or parts of the people controlling them being visible, and shadow/reflection effects being messed up. Some are obvious, others you only catch if you watch the clips frame-by-frame.
Walking with Monsters suffers from some particularly bad-looking CGI composition. A lot of times, animals either clip into the scenery, their shadows rarely correspond to the irregularities or the color of the ground, and in some shots, they are cropped a little bit too far from the screen's edge (like this poor fish◊), so you can even see parts of the background "through" them.*
Though this last one may depend on whether or not you watch it on DVD. At least one version of the Walking with Dinosaurs DVD also has some strange goings on at the edges of the screen.
Chased By Dinosaurs has the famous flying reptile Pteranodon living in the the earliest part of the Late Cretaceous (it really lived roughly in the middle) and in South America instead of North America. It was literally in the wrong place at the wrong time.
The Complete Guide cites Carnosauria as "an ill-defined collection of theropods, whose evolutionary relationships are much contested by scientists." This hasn't been the case since The Nineties at latest. Carnosauria is actually pretty well-defined and has been since the mid-nineties.
Special mention must go to Sea Monsters. It features pre-historic creatures underwater and interacting with Nigel.
The arena spectacular for the sheer spectacle of seeing life-sized dinosaurs live in front of you.
What Do You Mean, It's Not for Kids?: The series arguably was destined to a general public including both adults and children: however, for some people who watched it during childhood, several parts of the Walking With series are nothing but a long, endless sequence of Nightmare Fuel-related stuff. Arguably, talking about prehistory in a more reassuring way "will never be allowed" in TV. And the book "A Natural History" doesn't exactly better the situation, either.