There's no gradual revelation - the whole zombie plague scenario is expositionified in the first few seconds, plus some occasional flashbacks to flesh out the characters' backgrounds.
Zombieland is a fast zombie film in both senses - it's a fast-paced film featuring fast zombies. It's also witty, funny and endearing in turns, and if you can put up with a certain amount of ketchup and spaghetti, it's definitely one to watch even if zombies aren't usually your thing as the plot, the dialogue and the characters will win you over quickly. There's also a brilliant cameo by... no, better not say any more. I loved this film and I think it deserves it's many glowing reviews including a rare 89% score on Rotten Tomatoes.I understand George A. Romero's argument about zombie speed - they have to move slowly otherwise their rotting bones and tendons would break. But from a dramatic standpoint, fast zombies can provide a different kind of action. In Zombieland they're fast but not as superhumanly fast as seen in 28 Days Later. So you might outrun them - if you're lucky, and you've kept up Rule #1 of survival - Cardio. But even then it's not a done deal. This also means that a single fast zombie can be a threat - with slow zombies, since you can outrun them easily the threat only really builds up when they're massed. Of course, if you forget Rule #15 - Know your way out - and you get backed into a corner then the speed of the zombie may be less of an issue.
Zombie films often climax with some kind of siege - and Zombieland doesn't disappoint with it's ending set imaginatively in a theme park. Rule #33 might be, if you find yourself in a theme park during a zombie plague, don't turn on all the lights.