On the whole, zombie movies are not usually optimistic undertakings that send one smiling out of the theatre. However, there are exceptions.
Shaun of the Dead, of course, is the first film to come to mind, and deservedly so. The hero Shaun not only has to battle the living dead, armed only with a cricket bat, he also has to win back his girlfriend, get along with his stepfather, and please his mother while doing it. Simon Pegg as Shaun and Nick Frost as his slobby friend pull off the humor amidst the chaos of the world ending as only the British can.

Another older and overlooked film is
Night of the Comet. After a comet inexplicably vaporizes most of the population and zombifies the rest but for a lucky few, a pair of Valley girls make their way across the city to a radio station (which dates the movie big-time because a) are there still such things as Valley girls? and b) radio stations don't have the lure to young people they once had). Naturally, they run into obstacles when they get there, like an attractive young man who may be the last man on the planet, nasty psycho Goths, and a dark, deceitful government group. What really makes the movie work is that the sisters are so appealing (they are not airheads), and the movie has little twists that don't go in the direction you think they are going in.

Finally, the latest entry in upbeat zombie movies is
Zombieland. The audience is first introduced to a young man (Columbus) who is an outcast cursed with obssessive compulsive behavior and agoraphobia, two traits which render him an outcast in the normal world but aid his survival in Zombieland. He is our narrator who introduces us to the others he meets in his journeying: Tallahassee (played dead-on by Woody Harrelson), and a pair of sisters, Witchita and Little Rock. Tallahassee is a redneck zombie killer extraordinaire with an obsession with Twinkies, whereas Witchita and Little Rock are con artists with an obsession with getting to a Los Angles amusement park. There are many dry observations throughout the movie with on how to survive in a zombie world, a amazing and brillant cameo by Bill Murray, and a touching resolution that humans create their own families in a crisis.
All these movies have some brief gruesome gore scenes, which is a prerequisite for the genre. The writing is witty, the acting good, and zombie movies are an entertaining look at an end-of-the-world scenario.