And I don't think enough other people do. The debut feature from Eli Roth has so much going for it. Just a few reasons, off the top of my head...
The music. Nathan Barr does a fabulous nails-on-a-chalkboard score, starting with the gorgeous opening credits. Angelo Badalamenti contributes a jazzy, "Twin Peaks"-esque number for the surreal Deputy Winston, as well as the haunting "Red Love," for Paul's doomed attempt to manually satisfy Karen. A bunch of songs are borrowed from "Last House on the Left," providing both a shout-out to Roth's beloved 1970s horror, and setting a nicely creepy we're-alone-in-the-woods kind of mood.
I even love the closing bluegrass band, pepping up the end credits with "Swing Low, Sweet Chariot." (Apparently they were a local band and Roth invited them to come play in his movie; I just love that.)
The characters. They're all likable enough that you root for them, yet ultimately they're just rotten enough that you don't feel awful when they die. I've never seen a slasher movie that walks this line quite so well. They're selfish but not loathsome. Everyone gets annoyed with Burt when he shoplifts, and when Jeff talks down to the locals ("If such an incident were to result in a 'lawsuit,' you could be held liable"), his girlfriend Marcy tells him to shut up. A sick man asks for their help, and they light him on fire -- but they feel really bad about it! You wouldn't want to be on vacation with these kids, but you don't hate them like you hate the people in the "Friday the 13th" remake either.
The disease. Flesh-eating virus! I love nothing more than fake blood and zombie skin effects. I also love how a killer disease preys upon these beautiful, hygiene-hyperconscious kids -- "I don't want him touching me" is a recurring line. But the best part: Everyone gets sick by the end, but not one of the main characters actually dies of the disease.
The writing. "Paul, that guy asked for our help. We lit him on fire." (I also like when Jeff says "The rain probably put him out.")
The girl stuff. I might get in trouble for this but I think this movie is particularly fun for women. It can be hard to find good female characters in your modern horror movies; at a glance Marcy and Karen just fall into the usual slut/girl-next-door pigeonholes, but they turn out to be a lot more complicated. Marcy turns out to be very nurturing, fixing chili for everyone and stroking Karen's hair. Karen strings Paul along and then drops him as soon as a semi-cute stranger shows up with a bag of weed ("You can sit here!").
And I think women viewers just are going to get a more personal frisson out of Marcy's notorious leg-shaving sequence, or Paul's even more notorious misfire as he attempts to manually satisfy Karen. (Male viewers might relate to the misfire in their own way, of course.) Even just little moments ring true, like Karen talking about her parents' shower massage and saying "You can imagine my disappointment the first time I had sex." Marcy rolls her eyes: "Tell me about it," and all the boys look confused. ♥!
The group dynamics. People are awful, and they're even worse in groups. "Cabin Fever" is a fascinating showcase of groups behaving badly! First, the teenagers light the aforementioned sick man on fire. They don't mean to; they think he's attacking them, and maybe he is; but still, it's not nice. Later, when one of their group gets sick, they react in terror: screaming, running, slamming doors, and finally putting the sick girl outside in a shed, alone. I love the scene where they line up to carry her mattress out and then help her down the stairs, silent for the moment, their group decision made: they look like a tribunal, there on the back porch.
Then various group members go for help, running afoul of locals in various ways, then lying to each other about what happened: the group is coming apart. They meet their match in a tightly-knit, shotgun-toting family of rednecks. And that's before several law-enforcement agencies hold an emergency parley in a hospital room to discuss the best way to handle this strange new disease. It all seems chillingly plausible. I mean, we cover things up and scrub the surfaces clean and make sure our hair is as shiny as can be, but -- underneath it all, people are just nasty.
God, I love this movie.