Bottom line: Zombieland is a lot of fun if you can just accept it for what it is - just a fun zombie movie.
Now, Zombieland didn't supplant my all-time favorite zombie movie (Day of the Dead), heck it didn't crack the top 5, but it's still a lot of fun. In my book, any zombie movie is worth ten times its weight in regular action or horror movie fare, so I am biased.
The good about this movie is that it never takes itself too seriously like a Dawn of the Dead or 28 Days Later (both of which I loved and the former holds both spots 2 and 3 [for the remake] on my top-five list). It's almost always light-hearted (with a couple of sentimental moments) and often laugh-out-loud funny. It's got a great soundtrack. The movie opens with some old school Metallica - For Whom the Bell Tolls - and that helps set the mood. The ensemble cast was great. I haven't enjoyed Woody Harrelson this much in a long time. The last, and best IMHO, point is that it didn't try and make any statements. Nothing political or environmental. It just is what it is.
The bad. It drug in the beginning. I was really worried at moments. There was a lot of style - cool text overlays, high-def slow-mo camera tricks - and little substance. However, the story picked up quickly with the introduction of Harrelson's character. The other thing that bugged me, and I didn't think it would, is that this is another "running zombie" movie. I know a lot of people have issues with running zombies. I'm not one of them. I loved the Dawn of the Dead remake and think the fast zombies added a new level of suspense. 28 Days Later? I understand why they were running. This movie though, it just bugged me. I can't explain why.
If you can let certain things be certain things, then you will enjoy this movie better. I can't remember if we get a time frame on how long the zombiepocalypse has been going on, but I kept wondering why they still had electricity. It's something that's always bothered me about end-of-the-world-as-we-know-it movies. Power plants don't run themselves. They require a lot of people to keep 'em running. Small thing, really, but if you get stuck on things like that, this movie will stick you.
Aside from these relatively minor bad points, it was good. I enjoyed it. I'd give it three-and-a-half shambling corpses out of five.