Adaptation Displacement: Herbert West: Reanimator was written in 1921 and 1922, and Lovecraft was known to dislike the story; as such it was rarely reprinted and remained largely obscure for decades. The movie has almost completely supplanted it in popular culture.
Values Dissonance: There is an extremely racist description of a black boxer that would be considered disturbing to most modern-day readers.
It stretched the limits even for its day, being more like something you'd read in the Reconstruction-Era South than 1920's New England.
Alternative Character Interpretation: Herbert West is clearly insane, but how much of it is natural madness and how much of it is artificial psychosis induced by simultaneously forsaking sleep and regularly shooting up with a chemical compound of gods-know-what?
Ho Yay: While Herbert is more likely to be Asexual (even being confirmed by Jeffrey Combs), many fans have had fun interpreting his relationship with Dan like this, being akin to a Stalker with a Crush. Especially the scene where Herbert puts a blanket over Dan when he's rendered in shock after he Re-Animates Dr. Hemsley.
Contractual Immortality: Being played by Jeffrey Combs ensures that West survives the gory finale of each film against all odds— a sharp 180 degree inversion from the original novella, in which West ends up a victim of his reanimation subjects, torn to pieces by an undead mob.
Crosses the Line Twice: Okay, West killing Dr. Hill can be justified, he had it coming... But him decapitating him wholly and then re-animating the head and body separately for what amounts to shits and giggles? Seriously!
As usual, he justifies this with For Science!; he's never tried reanimating individual body parts before - and it works! Hill wakes up with his intelligence intact. Of course, bringing that guy of all people back was a bad idea, but at least it impacted how his research continued in Bride. This is actually directly adapted from the short story though there West did not kill the victim himself, but that was after decades of failed experiments when West's Motive Decay had begun to set in, not in the span of days like in the movie.
Slow-Paced Beginning: The entire purpose of the opening scene with the scientist's exploding head is because some crew members were worried the movie would otherwise take too long to get to the good stuff.
Squick: Plenty, but the scene where Dr. Hill brings a whole new meaning to the term "giving head" stands out in particular.
Special Effects Failure: The movie is actually really good in this regard, especially for a b-movie from the 1980's... with one glaring exception; Rufus the cat. The model they used isnt even slightly convincing and looks more like they disemboweled a rejected Muppet than a cat.