Player meta has been to lock every door in the bunker making any new visitors required to bring a lock pick, and hope they can open all the doors.
Some doors are metal which is hard or impossible to melee/shoot open.
The bunker doors with the wheel mechanism shouldn't be able to be locked.
I like the mechanic used to open at the exit, maybe in a future release create a control room with door switches like you'd see at a secure prison.
The operator can override/unlock doors remotely. DayZ doesn't have really any puzzles (do this to do that) unless you play a modded version Namalsk....
I saw on someones streams the valves and the water, that's a great addition to dayz!!!