Gwen isn't in Army of the Dead but supposedly she will show up in the sequel, so don't count her out yet. The Götterdämmerung heist is the premise for AotD. Basically, the vault with millions of dollars in it is in Las Vegas, which has been overrun by zombies, and the owner contracts a team to retrieve the money--or so it would seem--before the city is nuked. I think AotD would be a slog to watch if you're only in it for Dieter's part.