I also believe that the situation was avoidable. When Shane and Otis both went into the medical trailer, I immediately knew that it was going to be a mistake because there was no one outside to arrange the escape. That's one of the things that I think makes Shane more of a "villain," it's not just that he'll do whatever he thinks he needs to do to survive or help Carl and Lorie, it's that he's reckless. Instead of making a plan ahead of time, Shane just charged in, and when push came to shove, of course he fed Otis to the zombies.
Took my youngest (10) and her best friend to see it tonight, and wow, what a nostalgia trip! The girls loved it and thought it was hilarious. It was very much like the old specials and movies, borrowing themes directly from several of them.