One of the worst endings ever?

At first, the sudden ending surprised me, but it kind of worked.

They'd escaped the school, learned that the zombie problem was more widespread than they thought and learned that it was because of bad chicken nuggets. They speculated that a cure could be found, if they just found one of these nuggets. Yes, the fact that a chicken nugget was found several seconds after was a tad convenient, but in doing so the only thing left to achieve was to escape the arcade and start working on a cure.

The revelation that Wade was still alive and the escape was the last dramatic moment. Then they just had to find somewhere safe, and start working on the cure. They'd won.

We didn't really need to watch them working in a science lab, and then prescribing the cure to each child individually. That would've been dull.

It was meant as a comedy zombie film, and it worked on that front. It was always going to be slightly difficult to end when the main plot of the film was having them escape the school.