It's a great game, one thing i'd love to see is customizeable AI for your survivors, like telling your fighters to focus infected nearer a medic or someone else that's of importance.
Maybe just some improved AI for pathfinding when being attacked by infected. Mine often just run into a pack of infected and just keep running into them, getting bashed....
Maybe more options for automated missions.
Otherwise fantastic game, one of my definite favourites.