If you've never seen this spoof of a zombie film, you owe yourself as a writer to see it. Why? Not because it's brilliant, although it does have its moments, but because it's a great example of all those things that screenwriters are supposed to do. You want a three-act structure, with internal and external conflicts linked inexorably in a life-and-death struggle through the main character? He's right there. Trying to figure out how to build a main character around a strong desire and a single misbehavior? There he is. Want to see how to exploit character to develop backstory? Make him a bored, lazy TV salesman who doesn't actually hear what's being reported on the 32 televisions in the room.
One good thing about both spoofs and zombie films is that a key to their success is playing to audience expectations. You can't spoof a genre unless you portray it accurately. You can't have a zombie film without references to all the other zombie films.
This is valuable because the same basic three-act structure is used in everything from romantic comedies to action-adventures and historical epics. If you don't believe me, try a little experiment. Watch Shaun of the Dead. Stop the DVD every ten minutes or so, and write a sentence or two to describe what you've seen. You should have ten to twelve sentences. Now watch "Young Guns". Do the same thing. Now try "How Stella Got Her Groove Back." Look at when and how the main problem is introduced. Look at how the problem escalates every ten minutes. Look at how the main character grows. Look at the climax, and how it resolves the internal and external conflicts. Even when the problems are different, the answers all come from the same basic place.
I could also point to any number of really bad films with the same structure. It's not the fact of using this three-act structure that makes a film work. It's how you use it. If it's a tool that helps you develop something original and new, you're doing your job as a writer.