There is an aspect of zombie stories that is about wish fulfillment rather than horror. It's fantasy for people who like to imagine the complications of life being stripped down to its basic elements, where the rules no longer apply. Or in the case of Zombieland, have simply been replaced with a different set of all important rules.
Zombieland is another zombie comedy, but one that sets itself apart from previous ones like Shaun Of The Dead. Whereas Shaun is often about paying homage to classic zombie movies, Zombieland takes the zombie concept and just goes to town with all the wish fulfillment stuff. While the characters are often in peril, they don't spend most of their time cowering or running away. Rather, they seem to make the most of things. A huge section of the plot revolves around two of the characters making their way toward their favorite amusement park. Because if the world has ended you may as well ride a roller coaster or two.
And everyone seems to enjoy killing zombies for the most part. They even keep track of who had the best "Kill of the Week". Zombieland is generally an apocalyptic movie for optimists. In this world the geek can get the girl, you can hang out with your favorite celebrity (I won't reveal the amazing cameo, although it's unlikely it hasn't already been ruined for you), and you can smash and loot to your heart's content. The only downside seems to be that there is never a Twinkie around when you need one. Oh, and all your loved ones are dead (but let's not focus on that, shall we?).
Zombieland is an incredibly entertaining film (with a ton of potential sequels, apparently). I'm a huge zombie fan, and it's great to see such a fun, original take on things.