It needs an ending
I started playing the game yesterday because the idea intrigued me: can you humanize a zombie? As the plot progressed, tension was built up. Then, right at the point where the plot SHOULD climax, it just turns into a sandbox game. I'm gonna be honest, after putting 6 hours into the game and staying up until 3:30 in the morning to finish it, I felt ripped off.
I would argue that when you reach the final log and have 100% completion, something dramatic should happen to bring the story to a close. Maybe someone finds the bunker and you get rescued? Maybe the zombies break loose? Maybe you become infected after your long exposure to the zombies, because you slipped due to fatigue and got scratched? Hell, maybe you just simply run out of zombies and move on?
After putting as much time into playing the game as it takes to get to the end with 100% completion, there really should be a payoff. We gave you our time, you should give us some closure.