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.
The first film is notable for its entirely punk-rock soundtrack, particularly The Cramps' punk/surf rock-pastiche "Surfin' Dead", and for its clever and haunting use of Roky Erickson's "Burn The Flames"; see Murder by Cremation.
Ensemble Darkhorse: Tarman, who could be considered the mascot for the series as a whole. He is also the only character to have a toy made of him.
Ethnic Scrappy: The antagonists in the third movie consist of a group of offensive Mexican stereotypes.
Averted with Waterman, however. While, yes, he's a homeless black man, he's also genuinely compassionate, to the point that he can resist the hunger with effort, something only one other zombie in the franchise has done. What makes him more special than Frank is that Frank was converted from a living human, while Waterman was bitten to death by Julie before being reanimated, meaning he would probably be in worse pain.
Hell Is That Noise: Near the end of the movie, when the zombies mad dash to the barracade, there is a sound that they make that's so loud it's drowning out the phone call the Police Chief and Burt who was just trying to warn them about the approaching Zombies.
Memetic Mutation: Zombie movies changed after Return. Number one: zombies want braaaaaaiiiiiiiiiiiiiiins.
Older Than They Think: This series had fast zombies before fast zombies were cool. In fact, while not technically the first (the first zombie in Night of the Living Dead actually moves fairly quickly, and a film made five years before the first Return, called Nightmare City also had running zombies), it's arguably the first to really expose horror fans to running zombies.
Furthermore, while some zombies were shown using very simple tools in Night (one zombie uses a rock to smash in Barbara's car window, another uses a rock to smash the lights on Ben's car, Karen uses a trowel to stab someone to death), Return was the first big zombie film to depict zombies with logic skills, problem-solving skills and the ability to use sophisticated tools (see: Tarman using a chain and winch combination to rip the doors off of a cupboard to get Tina), predating Day of the Dead.
Sequelitis: The first is generally viewed as good, the second is viewed as a step down but an overall enjoyable movie, and the third is viewed as a good movie in the wrong series entirely. The fourth and fifth... they're Sci Fi Channel original movies.
Squick: The third movie. ESPECIALLY the unrated version, where things such as Julie ramming a glass shard through her palm are shown in horrific, unflinching detail.
Uncanny Valley: When they finally call the military number on the Trioxin Barrels in the first film. The main guy took it surprisingly well even though the people were responsible doomed an entire town. Subverted since the military was planning on dropping an A-bomb on them civilian and zombie alike.