Finger-Pickin? Good: Harrelson?s hick is a high point in Zombieland.

Drop Jesse Eisenberg into any role that Michael Cera’s landed over the past few years, and you’d hardly notice a hiccup. Both actors have a foal-like, please-shove-me-in-a-locker look. Both have become adept at playing virginal, dryly funny nerds who manage to get the girl only after putting in long hours of one-liners, self-deprecation, and uncool, knee-jerk sincerity. Both play these characters again and again and again.

So it’s little surprise that Eisenberg offers up another unlikely hero in Zombieland, Ruben Fleischer’s directorial debut about life in post-zombie-apocalyptic America. Not that there’s anything wrong with that. His Columbus, the apparently sole survivor in a small Texas town who’s convinced that his list of rules is the key to staying alive, is the perfect foil to the reluctant companion he runs into on his trek to Ohio: Tallahassee (Woody Harrelson), a maniacal Yosemite Sam of a man who loves guns, destruction, and directives such as “Time to nut up or shut up!” After nervously hitching a ride with Tallahassee, Columbus fastens his seat belt (one of his rules) and points out to Tallahassee, “You almost knocked over your alcohol with your knife.”

To be fair, all of the living are gun-happy here, even Wichita (Emma Stone) and her 12-year-old sister, Little Rock (Abigail Breslin), whom the guys repeatedly encounter (and get scammed by) as they seek out a zombie-free haven. We’re told only in passing how the undead came to be (according to Columbus’ voiceover, “mad cow equals mad person equals mad zombie”), and, unfortunately for purists, these zombies are zippy (which explains Columbus’ first rule: lots of cardio). As the foursome travel the country, there’s plenty of gore, bullets, and near-bites. And when they do find shelter, it’s never safe for very long.

But Zombieland is a straight-up comedy, even more so than its nearest relative, 2004’s occasionally frightful Shaun of the Dead. You may wonder, after that masterpiece as well as the 28 Days films and even George A. Romero’s return to his roots, 2007’s Diary of the Dead, whether it’s possible to add anything original to the zombie genre. The answer: Not really. This film’s strength is its humor, with a script by writers of no remarkable pedigree (Rhett Reese and Paul Wernick) that’s packed with movie references and goofy personalities—as when Little Rock watches Ghostbusters for the first time with Columbus, who tells her, “This is so exciting. You’re about to find out who you’re gonna call!”

Of course, there is also some great action, including the “zombie kill of the week” (which goes to a nun who flattens one with a piano) and Tallahassee’s killing spree on a roller coaster. With a machine gun. There’s also a whiff of a message via Columbus, a loner who admits to having “treated people like zombies before they were zombies” and never feeling a true sense of family. But above all else, Zombieland is fun—and no matter how many been-there monsters and done-that misfits are involved, such joyfulness will always feel fresh.