Nightmare Fuel: There's one scene where the Edmontosaurus are ambushed by the albertosaurs where one literally leaps (like a raptor) out of friggin' nowhere to tackle one of the poor plant-eaters. Imagine three tons of teeth and death leaping at you.
Not to mention that the filmmakers use slow motion to chilling effect in some of these scenes.
Nightmare Retardant: The appearence of the feathered tyrannosaurs can come across this way to some viewers, which isn't helped by the ridiculous Contrived Stupidity they often fall prey to in the program.
Special Effect Failure: The Troodon feathers very noticeably clip into their neck, and there is at least one Edmontosaurus that walks in the air.